Eastern California’s intense seismic and geothermal activity: Chicken or egg?

19 May 2016 | Send me Temblor Insights

A 13 May M=3.5 quake struck 30 mi (50 km) west of Death Valley at the northern tip of the Ash Hill fault. This quake is anything but an outlier: The ‘Walker Lane’ that extends between the eastern crest of the Sierra Nevada and into western Nevada was the site of the state’s third largest historical earthquake, in 1872, as well as some of the most vigorous seismic sequences in California since 1980. The Walker Lane accommodates 10-13 mm per year (0.5 in/yr) of right-lateral motion, about half of the San Andreas slip (Wesnousky, 2005), so by any measure is a major player in the Pacific-North American plate boundary.

A decade of seismicity reveals the strangely symmetrical distribution of earthquake clusters located beyond the ends of the 1872 Mw~7.6 earthquake. Both clusters enclose mixtures of hot springs, and extensional (‘normal’) faults and strike-slip faults, as well as sporadic eruptions in the past 12,000 or so years. Because of the hot springs, both have geothermal power plants. Several M>6 shocks struck in the 1980’s in the northern cluster, and several M~5 quakes struck in the 1990’s in the southern cluster.
A decade of seismicity reveals the strangely symmetrical distribution of earthquake clusters located beyond the ends of the 1872 Mw~7.6 earthquake. Both clusters enclose mixtures of hot springs, and extensional (‘normal’) faults and strike-slip faults, as well as sporadic eruptions in the past 12,000 or so years. Because of the hot springs, both have geothermal power plants. Several M>6 shocks struck in the 1980’s in the northern cluster, and several M~5 quakes struck in the 1990’s in the southern cluster.

The quake is a reminder that, despite all the press, California’s seismic hazard is not confined to the San Andreas. At the dawn of the plate tectonic revolution, the great Tanya Atwater first unraveled the 10 million year evolution of the San Andreas. Looking ahead to the next 10 million years, she argues that the Owens Valley and Death Valley faults will retire the San Andreas, as the plate boundary continues migrating to the East.

Here are two frames from an animation by Tanya Atwater, Professor Emeritus at U.C. Santa Barbara. The 13 May M=3.5 quake is one small step along the road to a vast transformation of the Pacific-North America plate boundary. Eventually, all of California will be head north toward Alaska, rather than only today’s coastal sliver of liberals. See https://youtu.be/9F8AcDJq2QU
Here are two frames from an animation by Tanya Atwater, Professor Emeritus at U.C. Santa Barbara. The 13 May M=3.5 quake is one small step along the road to a vast transformation of the Pacific-North America plate boundary. Eventually, all of California will be head north toward Alaska, rather than only today’s coastal sliver of liberals. See https://youtu.be/9F8AcDJq2QU

Was the 1872 rupture hemmed in by the geothermal zones, or did the rupture turn on the seismicity and hot water in these zones?

The 1872 rupture might reasonably have been confined between these two perhaps mushy, shattered, fluid-saturated zones. Or, these zones could have been turned on by the 1872 earthquake. This chicken-or-egg riddle would be easy to answer this if we knew whether or not the quake rate in these zones increased after the 1872 shock, but the mainshock predates seismometers, and few lived there.

Only one quake is known in the entire area before 1872, a M~5.5 event in July 1871 at the southern tip of the Owen’s Valley fault, shown as a star in the first map. This suggests the clusters might have been active before the mainshock. On the other hand, one of the two largest aftershocks of the 1872 event, a M~6.8 two weeks after the mainshock, stuck in the center of the northern cluster near Bishop (both are from Toppozada, Real, and Parke, 1981), also shown on the map. So, this would support the clusters being turned on by the mainshock. We walk away with a tie.

However, there is another clue to the riddle. The clusters lie in lobes where the 1872 rupture increased the shear stress and unclamped strike-slip faults. So, faults in the red zones below are brought closer to failure; in the blue zones they are inhibited from failure. This is called the ‘Coulomb failure stress;’ we made the calculation below in our free research software, Coulomb 3.4 (Shinji Toda et al., 2011).

Most of the past decade of shocks—but not last week’s M=3.5 event—lie in the Coulomb trigger zones imparted by the 1872 quake (the stresses are calculated using a reasonable but uncertain model of the rupture, based on the field mapping of the late and gifted Sarah Beanland and Malcolm Clark, 1994). The Coulomb trigger zones encompass the quakes beyond the ends of the 1872 rupture, and to a lesser extent, those extending to the east and west. But could stresses imparted 145 years ago still play a role today, or is this a phantom correlation?
Most of the past decade of shocks—but not last week’s M=3.5 event—lie in the Coulomb trigger zones imparted by the 1872 quake (the stresses are calculated using a reasonable but uncertain model of the rupture, based on the field mapping of the late and gifted Sarah Beanland and Malcolm Clark, 1994). The Coulomb trigger zones encompass the quakes beyond the ends of the 1872 rupture, and to a lesser extent, those extending to the east and west. But could stresses imparted 145 years ago still play a role today, or is this a phantom correlation?

Another way to assess the problem is to see if such intense off-fault clusters are found at other sites with geothermal activity. No better place to hunt for this than Iceland, with abundant earthquakes, eruptions, and geothermal power. The beautifully recorded 2008 Mw=6.0 South Iceland earthquake (Brandsdóttir et al., 2010; Decriem et al., 2010) shows clusters of aftershocks off the ends of the main rupture resembling Eastern California.

The figure is modified from Brandsdóttir et al. (2010), based on the fault inferred by Decriem et al. (2010). The aftershocks do indeed look like a small-scale version of contemporary seismicity surrounding the 1872 quake. The red ellipses enclose intense aftershock activity.
The figure is modified from Brandsdóttir et al. (2010), based on the fault inferred by Decriem et al. (2010). The aftershocks do indeed look like a small-scale version of contemporary seismicity surrounding the 1872 quake. The red ellipses enclose intense aftershock activity.

Could aftershocks persist for 150 years?

Even if the 1872 rupture triggered the activity in the clusters, it just begs a harder question: Could aftershocks continue almost 150 years after a mainshock? In fact, that question is very much alive in the New Madrid, Missouri, area, the site of vigorous seismicity today that some researchers think could be aftershocks of the still older 1811-1812 quakes, which were about the same size as the 1872 event.

What both sites have in common are active but slowly slipping faults; the Owens Valley fault slips at 2-3 mm/yr, about a tenth of the San Andreas rate. This means that at the aftershock sequence should be about ten times more drawn out than San Andreas aftershocks. The Owens Valley fault appears to fire off M~7.5 shocks roughly every 3,000-4,000 years (Lee et al., 2001), and so 150 years is several percent of the time between quakes, equivalent to about 15 years on the San Andreas, which is perhaps reasonable.

Owen’s Valley and Lone Pine buildings collapsed in 1872, courtesy of Laws Railroad Museum.
Owen’s Valley and Lone Pine buildings collapsed in 1872, courtesy of Laws Railroad Museum.
We owe the Sierran crest to the Lone Pine and Independence faults that bound the eastern Sierras from Owens Valley. (Photo by Barb Snyder, Egghillphotos, 2014)
We owe the Sierran crest to the Lone Pine and Independence faults that bound the eastern Sierras from Owens Valley. (Photo by Barb Snyder, Egghillphotos, 2014)

So, what is the role of the Owens Valley, Lone Pine, and Death Valley faults?

These extensional-right lateral faults, along with others to the north and south, lift up the highest peaks and depress the deepest valleys in California. Take away the faults, and we’d lose both Mount Whitney and Death Valley.  Give these faults a little time, and they will bound the vast Pacific and North American plates.

Ross Stein, Lester Lubetkin, and Volkan Sevilgen

You can check your home’s seismic risk at Temblor

Data from USGS, Nevada Seismological Laboratory (Univ. Nevada Reno), Tanya Atwater, and:

Sarah Beanland and Malcolm M. Clark (1994), The Owens Valley fault zone, eastern California, and surface faulting associated with the 1872 earthquake, U.S. Geol. Surv. Bulletin 1982, 29 p.

Bryndís Brandsdóttir, Parsons, M. and White, R. S. and Guðmundsson, O. and Drew, J. and Thorbjarnadóttir, B. (2010) The May 29 2008 earthquake aftershock sequence within the South Iceland Seismic Zone: Fault locations and source parameters of aftershocks. Jokull: journal of the glaciological and geological societies of Iceland, 60. pp. 23-46. ISSN 0449-0576

Judicael Decriem, T. Arnadottir, A. Hooper, H. Geirsson, F. Sigmundsson, M. Keiding, B. G. Ofeigsson, S. Hreinsdottir, P. Einarsson, P. LaFemina and R. A. Bennett (2010), The 2008 May 29 earthquake doublet in SW Iceland, Geophys. J. Int. 181, 1128–1146, doi: 10.1111/j.1365-246X.2010.04565.x

Jeffrey Lee, Joel Spencer, Lewis Owen (2001), Holocene slip rates along the Owens Valley fault, California: Implications for the recent evolution of the Eastern California Shear Zone, Geology, 29, 819–822.

Shine Toda, Ross S. Stein, Volkan Sevilgen, and Jian Lin (2011), Coulomb 3.3 Graphic-rich deformation and stress-change software for earthquake, tectonic, and volcano research and teaching-user guide. U.S. Geol. Surv. Open-File Rep. 2011-1060, ix, 54 p. (http://pubs.usgs.gov/of/2011/1060/)

Tousson R. Toppozada, C. R. Real, and D. L. Parke (1981). Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes, Calif. Div. Mines Geol. Open-File Rept. 81-11 SAC, 182 pp (Interactive historical earthquake map, http://maps.conservation.ca.gov/cgs/historicearthquakes/

Steven G. Wesnousky (2005), Active faulting in the Walker Lane, Tectonics, 24, doi:10.1029/2004TC001645.

Is the San Andreas “locked, loaded, and ready to go”?

10 May 2016  |  Editorial  |   Send me Temblor Insights

Volkan and I presented and exhibited Temblor at the National Earthquake Conference in Long Beach last week. Prof. Thomas Jordan, USC University Professor, William M. Keck Foundation Chair in Geological Sciences, and Director of the Southern California Earthquake Center (SCEC), gave the keynote address. Tom has not only led SCEC through fifteen years of sustained growth and achievement, but he’s also launched countless initiatives critical to earthquake science, such as the Uniform California Earthquake Rupture Forecasts (UCERF), and the international Collaboratory for Scientific Earthquake Predictability (CSEP), a rigorous independent protocol for testing earthquake forecasts and prediction hypotheses.

In his speech, Tom argued that to understand the full range and likelihood of future earthquakes and their associated shaking, we must make thousands if not millions of 3D simulations. To do this we need to use theTom Jordan portrait next generation of super-computers—because the current generation is too slow! The shaking can be dramatically amplified in sedimentary basins and when seismic waves bounce off deep layers, features absent or muted in current methods. This matters, because these probabilistic hazard assessments form the basis for building construction codes, mandatory retrofit ordinances, and quake insurance premiums. The recent Uniform California Earthquake Rupture Forecast Ver. 3 (Field et al., 2014) makes some strides in this direction. And coming on strong are earthquake simulators such as RSQsim (Dieterich and Richards-Dinger, 2010) that generate thousands of ruptures from a set of physical laws rather than assumed slip and rupture propagation. Equally important are CyberShake models (Graves et al., 2011) of individual scenario earthquakes with realistic basins and layers.

But what really caught the attention of the mediaand the public—was just one slide

Tom closed by making the argument that the San Andreas is, in his words, “locked, loaded, and ready to go.” That got our attention. And he made this case by showing one slide. Here it is, photographed by the LA Times and included in a Times article by Rong-Gong Lin II that quickly went viral.

Source: http://www.latimes.com/local/lanow/la-me-ln-san-andreas-fault-earthquake-20160504-story.html
Source: http://www.latimes.com/local/lanow/la-me-ln-san-andreas-fault-earthquake-20160504-story.html

Believe it or not, Tom was not suggesting there is a gun pointed at our heads. ’Locked’ in seismic parlance means a fault is not freely slipping; ‘loaded’ means that sufficient stress has been reached to overcome the friction that keeps it locked. Tom argued that the San Andreas system accommodates 50 mm/yr (2 in/yr) of plate motion, and so with about 5 m (16 ft) of average slip in great quakes, the fault should produce about one such event a century. Despite that, the time since the last great quake (“open intervals” in the slide) along the 1,000 km-long (600 mi) fault are all longer, and one is three times longer. This is what he means by “ready to go.” Of course, a Mw=7.7 San Andreas event did strike a little over a century ago in 1906, but Tom seemed to be arguing that we should get one quake per century along every section, or at least on the San Andreas.

Could it be this simple?

Now, if things were so obvious, we wouldn’t need supercomputers to forecast quakes. In a sense, Tom’s wake-up call contradicted—or at least short-circuited—the case he so eloquently made in the body of his talk for building a vast inventory of plausible quakes in order to divine the future. But putting that aside, is he right about the San Andreas being ready to go?

Because many misaligned, discontinuous, and bent faults accommodate the broad North America-Pacific plate boundary, the slip rate of the San Andreas is generally about half of the plate rate. Where the San Andreas is isolated and parallel to the plate motion, its slip rate is about 2/3 the plate rate, or 34 mm/yr, but where there are nearby parallel faults, such as the Hayward fault in the Bay Area or the San Jacinto in SoCal, its rate drops to about 1/3 the plate rate, or 17 mm/yr. This means that the time needed to store enough stress to trigger the next quake should not—and perhaps cannot—be uniform. So, here’s how things look to me:

The San Andreas (blue) is only the most prominent element of the 350 km (200 mi) wide plate boundary. Because ruptures do not repeat—either in their slip or their inter-event time—it’s essential to emphasize that these assessments are crude. Further, the uncertainties shown here reflect only the variation in slip rate along the fault. The rates are from Parsons et al. (2014), the 1857 and 1906 average slip are from Sieh (1978) and Song et al. (2008) respectively. The 1812 slip is a model by Lozos (2016), and the 1690 slip is simply a default estimate.
The San Andreas (blue) is only the most prominent element of the 350 km (200 mi) wide plate boundary. Because ruptures do not repeat—either in their slip or their inter-event time—it’s essential to emphasize that these assessments are crude. Further, the uncertainties shown here reflect only the variation in slip rate along the fault. The rates are from Parsons et al. (2014), the 1857 and 1906 average slip are from Sieh (1978) and Song et al. (2008) respectively. The 1812 slip is a model by Lozos (2016), and the 1690 slip is simply a default estimate.

So, how about ‘locked, generally loaded, with some sections perhaps ready to go’

When I repeat Tom’s assessment in the accompanying map and table, I get a more nuanced answer. Even though the time since the last great quake along the southernmost San Andreas is longest, the slip rate there is lowest, and so this section may or may not have accumulated sufficient stress to rupture. And if it were ready to go, why didn’t it rupture in 2010, when the surface waves of the Mw=7.2 El Major-Cucapah quake just across the Mexican border enveloped and jostled that section? The strongest case can be made for a large quake Nicolas Ambraseysoverlapping the site of the Great 1857 Mw=7.8 Ft. Teton quake, largely because of the uniformly high San Andreas slip rate there. But this section undergoes a 40° bend (near the ‘1857’ in the map), which means that the stresses cannot be everywhere optimally aligned for failure: it is “locked” not just by friction but by geometry.

A reality check from Turkey

Sometimes simplicity is a tantalizing mirage, so it’s useful to look at the San Andreas’ twin sister in Turkey: the North Anatolian fault. Both right-lateral faults have about the same slip rate, length, straightness, and range of quake sizes; they both even have a creeping section near their midpoint. But the masterful work of Nicolas Ambraseys, who devoured contemporary historical accounts along the spice and trade routes of Anatolia to glean the record of great quakes (Nick could read 14 languages!) affords us a much longer look than we have of the San Andreas.

The idea that the duration of the open interval can foretell what will happen next loses its luster on the North Anatolian fault because it’s inter-event times, as well as the quake sizes and locations, are so variable. If this 50% variability applied to the San Andreas, no sections could be fairly described as ‘overdue’ today. Tom did not use this term, but others have. We should, then, reserve ‘overdue’ for an open interval more than twice the expected inter-event time.

This figure of North Anatolian fault quakes is from Stein et al. (1997), updated for the 1999 Mw=7.6 Izmit quake, with the white arrows giving the direction of cascading quakes. Even though 1939-1999 saw nearly the entire 1,000 km long fault rupture in a largely western falling-domino sequence, the earlier record is quite different. When we examined the inter-event times (the time between quakes at each point along the fault), we found it to be 450±220 years. Not only was the variation great—50% of the time between quakes—but the propagation direction was also variable.
This figure of North Anatolian fault quakes is from Stein et al. (1997), updated for the 1999 Mw=7.6 Izmit quake, with the white arrows giving the direction of cascading quakes. Even though 1939-1999 saw nearly the entire 1,000 km long fault rupture in a largely western falling-domino sequence, the earlier record is quite different. When we examined the inter-event times (the time between quakes at each point along the fault), we found it to be 450±220 years. Not only was the variation great—50% of the time between quakes—but the propagation direction was also variable.

However, another San Andreas look-alike, the Alpine Fault in New Zealand, has a record of more regular earthquakes, with an inter-event variability of 33% for the past 24 prehistoric quakes (Berryman et al., 2012). But the Alpine fault is straighter and more isolated than the San Andreas and North Anatolian faults, and so earthquakes on adjacent faults do not add or subtract stress from it. And even though the 31 mm/yr slip rate on the southern Alpine Fault is similar to the San Andreas, the mean inter-event time on the Alpine is longer than any of the San Andreas’ open intervals: 330 years. So, while it’s fascinating that there is a ‘metronome fault’ out there, the Alpine is probably not a good guidepost for the San Andreas.

If Tom’s slide is too simple, and mine is too equivocal, what’s the right answer?

I believe the best available answer is furnished by the latest California rupture model, UCERF3. Rather than looking only at the four San Andreas events, the team created hundreds of thousands of physically plausible ruptures on all 2,000 or so known faults. They found that the mean time between Mw≥7.7 shocks in California is about 106 years (they report an annual frequency of 9.4 x 10^-3 in Table 13 of Field et al., 2014; Mw=7.7 is about the size of the 1906 quake; 1857 was probably a Mw=7.8, and 1812 was probably Mw=7.5). In fact, this 106-year interval might even be the origin of Tom’s ‘once per century’ expectation since he is a UCERF3 author.

But these large events need not strike on the San Andreas, let alone on specific San Andreas sections, and there are a dozen faults capable of firing off quakes of this size in the state. While the probability is higher on the San Andreas than off, in 1872 we had a Mw=7.5-7.7 on the Owen’s Valley fault (Beanland and Clark, 1994). In the 200 years of historic records, the state has experienced up to three Mw≥7.7 events, in southern (1857) and eastern (1872), and northern (1906) California. This rate is consistent with, or perhaps even a little higher than, the long-term model average.

So, what’s the message

While the southern San Andreas is a likely candidate for the next great quake, ‘overdue’ would be over-reach, and there are many other fault sections that could rupture. But since the mean time between Mw≥7.7 California shocks is about 106 years, and we are 110 years downstream from the last one, we should all be prepared—even if we cannot be forewarned.

Ross Stein (ross@temblor.net), Temblor

You can check your home’s seismic risk at Temblor

References cited:

Sarah Beanland and Malcolm M. Clark (1994), The Owens Valley fault zone, eastern California, and surface faulting associated with the 1872 earthquake, U.S. Geol. Surv. Bulletin 1982, 29 p.

Kelvin R. Berryman, Ursula A. Cochran, Kate J. Clark, Glenn P. Biasi, Robert M. Langridge, Pilar Villamor (2012), Major Earthquakes Occur Regularly on an Isolated Plate Boundary Fault, Science, 336, 1690-1693, DOI: 10.1126/science.1218959

James H. Dietrich and Keith Richards-Dinger (2010), Earthquake recurrence in simulated fault systems, Pure Appl. Geophysics, 167, 1087-1104, DOI: 10.1007/s00024-010-0094-0.

Edward H. (Ned) Field, R. J. Arrowsmith, G. P. Biasi, P. Bird, T. E. Dawson, K. R., Felzer, D. D. Jackson, J. M. Johnson, T. H. Jordan, C. Madden, et al.(2014). Uniform California earthquake rupture forecast, version 3 (UCERF3)—The time-independent model, Bull. Seismol. Soc. Am. 104, 1122–1180, doi: 10.1785/0120130164.

Robert Graves, Thomas H. Jordan, Scott Callaghan, Ewa Deelman, Edward Field, Gideon Juve, Carl Kesselman, Philip Maechling, Gaurang Mehta, Kevin Milner, David Okaya, Patrick Small, Karan Vahi (2011), CyberShake: A Physics-Based Seismic Hazard Model for Southern California, Pure Appl. Geophysics, 168, 367-381, DOI: 10.1007/s00024-010-0161-6.

Julian C. Lozos (2016), A case for historical joint rupture of the San Andreas and San Jacinto faults, Science Advances, 2, doi: 10.1126/sciadv.1500621.

Tom Parsons, K. M. Johnson, P. Bird, J.M. Bormann, T.E. Dawson, E.H. Field, W.C. Hammond, T.A. Herring, R. McCarey, Z.-K. Shen, W.R. Thatcher, R.J. Weldon II, and Y. Zeng, Appendix C—Deformation models for UCERF3, USGS Open-File Rep. 2013–1165, 66 pp.

Seok Goo Song, Gregory C. Beroza and Paul Segall (2008), A Unified Source Model for the 1906 San Francisco Earthquake, Bull. Seismol. Soc. Amer., 98, 823-831, doi: 10.1785/0120060402

Kerry E. Sieh (1978), Slip along the San Andreas fault associated with the great 1857 earthquake, Bull. Seismol. Soc. Am., 68, 1421-1448.

Ross S. Stein, Aykut A. Barka, and James H. Dieterich (1997), Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering, Geophys. J. Int., 128, 594-604, 1997, 10.1111/j.1365-246X.1997.tb05321.x

Kentucky Magnitude-3.5 quake highlights the liquefaction potential in the disputed New Madrid seismic zone

1 May 2016  |  Quake Insights

Today’s earthquake lies at the northern end of the New Madrid seismic zone, which ruptured in three Magnitude-7 or greater earthquakes in the winter of 1811-1812. The events occurred a few weeks apart on December 16, January 23, and February 7. They damaged the frontier communities in the area and were felt throughout the central and eastern U.S (Hough and Page, 2011). Sand blows, where water shoots through the soil and erupts at the surface, and other evidence of severe liquefaction, occurred in the water-saturated sediments of the Mississippi Embayment. Perhaps remote aftershocks, a M~6.3 quake struck the southwestern end of the seismic zone in Arkansas in 1843, and a M~6.6 struck northeastern end in Charleston, Missouri in 1895, just 30 mi (50 km) southwest of today’s shock. 

Last week, Temblor added liquefaction maps for KY, TN, IL, MO, and AK, so that homeowners in the greater New Madrid Seismic Zone could assess this important source of seismic risk. If one’s home sinks or tilts in an earthquake due to earthquake-triggered liquefaction, even a well-built home can suffer a total loss.
Last week, Temblor added liquefaction maps for KY, TN, IL, MO, and AK, so that homeowners in the greater New Madrid Seismic Zone could assess this important source of seismic risk. If one’s home sinks or tilts in an earthquake due to earthquake-triggered liquefaction, even a well-built home can suffer a total loss.
The figure is from Eric Calais, Andy Freed, Roy Van Arsdale, and Seth Stein (Nature, 2010), showing 1974-2010 earthquakes from the Center for Earthquake Research and Information (CERI) University of Memphis catalog. The faults are inferred from the seismicity alignments. The Mississippi Embayment is a deep bowl of water-saturated river sediments that are most susceptible to liquefaction.
The figure is from Eric Calais, Andy Freed, Roy Van Arsdale, and Seth Stein (Nature, 2010), showing 1974-2010 earthquakes from the Center for Earthquake Research and Information (CERI) University of Memphis catalog. The faults are inferred from the seismicity alignments. The Mississippi Embayment is a deep bowl of water-saturated river sediments that are most susceptible to liquefaction.

Prehistoric sand blows have been dated to the 1400’s and ~900 A.D, and interpreted as evidence for similar events, potentially making the area north of Memphis one of the most seismically active sites in the U.S; this is evident in USGS hazard maps and so also in Temblor.

But there’s a catch

There is no geodetically measurable strain at the earth’s surface across this active fault system, as has most recently been confirmed by Craig and Calais (2014). How can a fault fire off M~7 quakes every 500 or so years if there is no strain accumulation? Our hard-won understanding of how faults work is this: The surface strain is the product of the stresses that drive fault slip at depth. The slip is resisted by fault friction, and so only when the stress reaches some threshold is the friction overcome in earthquakes. The higher the rate of stress accumulation, the higher the earthquake rate; the larger or longer the fault, the larger the maximum quake that can rupture on it. It’s that simple.

sand blows

Do sand blows record only local events?

Paleoseismologists are confident that the age dating of the sand blows is sound (Tuttle et al, 2006). But when a sand blow erupted in Thousand Springs Valley in the 1983 M=6.9 Borah Peak, ID, quake, it ejected old Cracker Jack boxes onto the ground surface. These 1960’s relics turned out to be trash that the locals had thrown into the crater after it formed during the 1959 M=7.3 Hebgen Lake, MT, quake. But Hebgen Lake quake struck 140 mi (225 km) away. So, in our judgment, sand blows need not be evidence of a local quake; they might instead be triggered when seismic waves excite mushy soil far away. Perhaps, then, the bullseye of high hazard in the USGS model should instead be spread out over a far wider area. If this were the case, the absence of strain accumulation would still be a mystery, but it would be much less difficult to reconcile if a far broader network of faults were being very slowly strained, and the faults that ruptured in 1811-1812 unlikely to do so again for thousands of years, with others rupturing next.

The hazard could be concentrated but more likely is diffuse

Whether or not the New Madrid, MO, area is the site of the very high seismic hazard in the U.S. remains a fiercely debated topic at just about every Fall meeting of American Geophysical Union and in the literature. The region is highly active today, although these shocks may be part of a very long-lived aftershock sequence that began in 1811 that will continue to slowly decay. If large earthquakes throughout the Mississippi Embayment and Wabash Valley areas are capable triggering sand blows in New Madrid, then at the very least, the area stretching from Memphis to central Illinois has a significant seismic hazard.

Ross Stein, David Jacobson, and Volkan Sevilgen, Temblor

Data from USGS, Center for Earthquake Research and Information (CERI), University of Memphis,  E. Calais, A. M. Freed, R. Van Arsdale & S. Stein, Triggering of New Madrid seismicity by late-Pleistocene erosion, Nature, 466, doi:10.1038/nature09258 (2010); Craig, T.J., and E. Calais (2014), Strain accumulation in the New Madrid and Wabash Valley seismic zones from 14 years of continuous GPS observation, J. Geophys. Res., 119, 9110–9129, doi:10.1002/2014JB011498; Hough, S. E., and M. Page (2011), Toward a consistent model for strain accrual and release for the New Madrid Seismic Zone, central United States, J. Geophys. Res., 116, B03311, doi:10.1029/2010JB007783; Martitia P. Tuttle, Haydar Al-Shukri, Hanan Mahdi (2006), Very Large Earthquakes Centered Southwest of the New Madrid Seismic Zone 5,000–7,000 Years Ago, Seismol. Res. Letts., 77, doi: 10.1785/gssrl.77.6.755, Central US Earthquake Consortium, Arkansas Geologic Survey, Indiana Geologic Survey

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Imperial seismic swarm lights up the southern tip of the San Jacinto fault in an area of extreme hazard

22 April 2016  |  Quake Insights

A seismic burst, so far topped only by a M=3.4 shock, struck beneath the city of Imperial yesterday. It’s a fascinating location, where the San Andreas fault system converges with the San Jacinto fault system.

The great San Andreas and San Jacinto fault systems somehow merge in the deep, sediment-filled Salton trough. The size and year of historical earthquake ruptures are shown in blue.
The great San Andreas and San Jacinto fault systems somehow merge in the deep, sediment-filled Salton trough. The size and year of historical earthquake ruptures are shown in blue.

The site of the recent swarm is surrounded by the rupture zones of recent large earthquakes, and so has among the highest Temblor seismic hazard ranks in the U.S. Those shocks include the overlapping 1940 M=6.9 and 1979 M=6.4 Imperial Valley earthquakes, the 1987 M=6.6 Superstition Hills earthquake, the 2010 M=7.2 El Mayor-Cucapah quake, which was largely in Baja California but just crossed the border into the US (the Mexican geologists jokingly referred to it as an ‘illegal fault’), and the 26 August 2012 M≤5.4 Brawley Seismic swarm, on a linking cross fault.

In this Google Earth image, the sites where the San Andreas and San Jacinto systems diverge (north of Riverside) and converge (south of Imperial) are seen. Julian Lozos’ interpretation of the 1812 rupture is also shown. This event collapsed or highly damaged Missions San Juan Capistrano and San Gabriel, and caused minor damage at Missions San Fernando and San Buenaventura. The image is 325 km (175 mi) across.
In this Google Earth image, the sites where the San Andreas and San Jacinto systems diverge (north of Riverside) and converge (south of Imperial) are seen. Julian Lozos’ interpretation of the 1812 rupture is also shown. This event collapsed or highly damaged Missions San Juan Capistrano and San Gabriel, and caused minor damage at Missions San Fernando and San Buenaventura. The image is 325 km (175 mi) across.

Julian Lozos, now at California State University Northridge and formerly a USGS post-Doc, published an article last month in Science Advances arguing that the enigmatic 8 Dec 1812 M~7.5 shock most likely ruptured the San Jacinto fault north of Riverside, but then jumped onto the San Andreas fault. This and another evidence suggests that fault jumps in the San Andreas system are not only possible but likely. This jump took place 150 mi (235 km) northwest of where the two faults converge near Imperial, site of the recent swarm.

The 21 April 2016 swarm struck on the periphery of Imperial (grey area), with 16,000 residents.
The 21 April 2016 swarm struck on the periphery of Imperial (grey area), with 16,000 residents.

Could another large quake re-rupture the Superstition Hills fault, or jump on to the Brawley seismic zone?

The Brawley is an unusual section of the San Andreas without surface expression, but the site of many swarms and fault creep events at depth. Although how these faults connect at depth is unclear, what is indisputable is that major faults and perpendicular ‘cross-faults’ can be activated simultaneously as occurred in 1987 (Hudnut et al., 1989), so there are a myriad of potential linkages that put the cities of Imperial, El Centro, Brawley, Westmoreland, and Mexicali, and the rich surrounding agricultural areas, at risk.

Ross Stein and Volkan Sevilgen, Temblor

Data from Caltech/USGS Southern California Seismic Network, USGS, and California Geological Survey, Southern California Earthquake Center, and:

Julian C. Lozos (2016), A case for historical joint rupture of the San Andreas and San Jacinto faults, Sci. Adv., 2, doi: 10.1126/sciadv.1500621.

Kenneth W. Hudnut, L. Seeber, and J.Pacheco (1989), Cross-fault triggering in the November 1987 Superstition Hills earthquake sequence, southern California, Geophys. Res. Letts., 16, doi: 10.1029/GL016i002p00199

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16 April 2016 Ecuador M=7.8 quake likely a repeat of a 1942 M=7.8 shock; such repeats are rare but important

17 April 2016  |  Quake Insights

The event severely shook the coastal cities of Muisne, Tosagua, and Pedernales, with 34,000 inhabitants. The quake was broadly felt throughout Ecuador and southern Colombia. On the basis of historic earthquakes, including the 1906 M~8.3 shock, as well as a high strain rate, the region was known to have a high seismic hazard.

The megathrust ruptured along the Ecuador Trench, along which the Nazca plate subjects beneath South America at about 55-61 mm/yr. The rupture area, as determined thus far only by Gavin Hayes at the USGS in Golden, CO, using seismic waveforms, is about 50 x 100 km in extent (30 x 60 mi), and is inclined (‘dipping’) at about 15° under the coastline. The rupture propagation took about a minute, with the greatest pulse in the first 30 seconds. The peak slip is about 5 m (16 ft), directly under the coastline. The shallow depth, rapid rupture, and high slip beneath populated areas probably all contributed to the damage, which thus far has killed 238, and will likely rise considerably.

Rupture areas of historical quakes near the 20 April 2016 M=7.8 event. The 1942 rupture area nearly coincides with the 2016 quake. There was also a M=7.1 shock in 1998 (Chlieh et al., 2014), which lies within, or just south of, today’s aftershocks. The 2016 event could also trigger a a subsequent megathrust quake to the north, or on the right-lateral Jama-Quininde fault (Collot et al. 2004).
Rupture areas of historical quakes near the 16 April 2016 M=7.8 event. The 1942 rupture area nearly coincides with the 2016 quake. There was also a M=7.1 shock in 1998 (Chlieh et al., 2014), which lies within, or just south of, today’s aftershocks. The 2016 event could also trigger a a subsequent megathrust quake to the north, or on the right-lateral Jama-Quininde fault (Collot et al. 2004).

The 16 April 2016 quake appears to lie in almost the exact location as the 1942 M=7.8 quake studied by Senneson and Beck (1998). The distribution of observed seismic intensities for the 1942 shock closely match those predicted by the USGS for yesterday’s quake, and their aftershock distributions are similar. In addition, the large aftershocks of the 16 April 2016 shock lie on either side of the 1942 rupture zone. This would be expected if the 2016 rupture were smooth (rather than spiky), with aftershocks in the Coulomb stress ‘butterfly zones’ just outside of the rupture patch.

The ISC-GEM seismic catalog shows that the M=7.8 epicenter is surrounded by large quakes over the past century, whereas in southern Ecuador, there have been no great quakes (top). Nevertheless, the strain rate is high along the entire Ecuador coastline (bottom). This part of the boundary could slip aseismically, or in less frequent but larger earthquakes. These invaluable datasets were produced by the GEM Foundation, which is building a seismic risk model for the world, and is currently working on its Ecuador model together with South American scientists.
The ISC-GEM seismic catalog shows that the M=7.8 epicenter is surrounded by large quakes over the past century, whereas in southern Ecuador, there have been no great quakes (top). Nevertheless, the strain rate is high along the entire Ecuador coastline (bottom). This part of the boundary could slip aseismically, or in less frequent but larger earthquakes. These invaluable datasets were produced by the GEM Foundation, which is building a seismic risk model for the world, and is currently working on its Ecuador model together with South American scientists.

There is also evidence that 50 km to the south of the 2016 M=7.8 quake, there was a ‘slow slip event,’ essentially a M=6.3 silent earthquake. This event is shown in the figure below from Chlieh et al. (2014); the event can only be detected by GPS receivers because it did not excite any seismic waves. Many subduction zones produce such slow slip events. It is possible that theses events, if frequent enough, relieve the stress that would otherwise accumulate to produce great quakes.

In this figure from Chlieh et al (2014), ‘ISC’ means inter-seismic coupling. If it is red (1.0), the megathrust is stuck and must produce quakes; if blue (0.0), the plate is freely slipping and so large quakes will not strike. Notice that this model shows the site of the 2016 quake is blue (at the site of the 1942 star), which the quake just proved incorrect. Science is hard.
In this figure from Chlieh et al (2014), ‘ISC’ means inter-seismic coupling. If it is red (1.0), the megathrust is stuck and must produce quakes; if blue (0.0), the plate is freely slipping and so large quakes will not strike. Notice that this model shows the site of the 2016 quake is in the blue (at the site of the 1942 star), which means this 2016 quake just disproved this ICS theory. Science is hard.

Is a repeat of the 1942 event reasonable, given that only 75 years has since elapsed?

The answer is yes. At the 60 mm/yr subduction rate, 75 years is enough to produce another quake with 4-5 m (12-16 ft) of slip. Given the area of the two shocks, a M=7.8 today would be right on target if the site did not suffer much larger quakes at other times. But that’s the problem: The site did suffer a M~8.3 event in 1906, and so repeats of M=7.8 events cannot be the whole story. Near-exact repeats of earthquakes are very rare; in general, we find a wide diversity of rupture behavior. And considering that this site was part of the ten-times larger event in 1906, it is particularly baffling.

What next?

A subsequent M~8 event to the south might be considered unlikely, both because of the M=7.1 event in 1998 and the slow slip event in 2010. But the region to the north of the 16 April 2016 event is different. There is an 80 km (50 mi) region that has not ruptured since 1906 that would seem able to host another M~7.8 shock. Further, there is the right-lateral Jama-Quininde fault, parts of which could have been brought closer to Coulomb failure by this recent 2016 megathrust event. Both should now be closely watched.

Correction: The date of the M=7.8 is Apr 16, 2016, was written as Apr 20, 2016 in the earlier versions.  

Ross Stein and Volkan Sevilgen, Temblor

Sources: USGS, GEM Foundation (globalquakemodel.org), and,

Chlieh, M., P.A. Mothes, J.-M. Nocquet, P. Jarrin, P. Charvis, D. Cisneros, Y. Font, J.-Y. Collot, J.-C. Villegas-Lanza, F. Rolandone, M. Vallée, M. Regnier, M. Segovia, X. Martin, H. Yepes (2014), Distribution of discrete seismic asperities and aseismic slip along the Ecuadorian megathrust, Earth Planet. Sci. Letts., 400, 292-301, http://dx.doi.org/10.1016/j.epsl.2014.05.027

Collot, J.-Y., B. Marcaillou, F. Sage, F. Michaud, W. Agudelo, P. Charvis, D. Graindorge, M.-A. Gutscher, and G. Spence (2004), Are rupture zone limits of great subduction earthquakes controlled by upper plate structures? Evidence from multichannel seismic reflection data acquired across the northern Ecuador–southwest Colombia margin, J. Geophys. Res., 109, B11103, doi:10.1029/2004JB003060.

Sennson, Jennifer L, and Susan L. Beck (1996), Historical 1942 Ecuador and 1942 Peru subduction earthquakes and earthquake cycles along Colombia-Ecuador and Peru subduction segments Pure Appl. Geophys., 146, 67-101, doi: 10.1007/BF00876670

The Tail that Wagged the Dog: M=7.0 Kumamoto, Japan shock promoted by M=6.1 quake that struck 28 hr beforehand

16 April 2016  |  Quake Insights

A Mw=6.1 earthquake struck on April 14, followed by vigorous aftershocks. The epicenter as determined by the Japan Meteorological Agency (JMA) lies approximately where the ‘right-lateral’ (San Andreas-like) Hinagu and Futagawa faults meet, on the eastern edge of Kumamoto, a city of 700,000 people on the island of Kyushu in southwest Japan. The quake was followed today by a Mw=7.0 quake that may have ruptured parts of both fault systems. The events were shallow (10-12 km or 6-8 mi deep), both were destructive, but the second quake was about twenty times larger than the first one. How large is a Mw=7.0 quake?

In a moment of modern madness, on 9 August 1945 an atomic bomb was dropped on Nagasaki, just 70 km (40 mi) west of Kumamoto, killing 60,000-80,000 citizens. The energy released by today’s M=7.0 earthquake was 400,000 times greater.

Aftershock map (made without using the local JMA network so inaccurate, at 5 pm PDT on 16 Apr) shows the much larger area of the M=7.0 aftershocks, which extend well to the northeast
Aftershock map (made without using the local JMA network so inaccurate, at 5 pm PDT on 16 Apr shows the much larger area of the M=7.0 aftershocks, which extend well to the northeast

The Mw=7.0 event is about 40 km (25 miles) long, may have ruptured to the earth’s surface, and appears to have propagated largely to the northeast. The evidence for the propagation are the seismograms that Gavin Hayes at the USGS in Golden, CO, used to infer the distribution of fault slip, and also the very high shaking (‘peak ground accelerations’) seen as much as 50 km (30 mi) to the northeast of the mainshock. Typical wood frame homes in the US and Japan can begin to suffer structural damage at peak ground accelerations of about 0.40 g (40% of the acceleration of gravity), but values twice that high are seen both near the epicenter and 50 km to the northeast. If these are representative, there will be significant damage over a broad area.

Preliminary map of observed (triangles) and inferred (contours) shaking from the Mw=7.0 event, from the USGS. The contours blend a model and data. The shaking appears to be much stronger to the northeast, suggesting how the 40 km long fault ruptured (or, unzipped).
Preliminary map of observed (triangles) and inferred (contours) shaking from the Mw=7.0 event, from the USGS. The contours blend a model and data. The shaking appears to be much stronger to the northeast, suggesting how the 40 km long fault ruptured (or, unzipped).

 

The excellent J-SHIS Japanese seismic hazard app is available in the App Store
The excellent J-SHIS Japanese seismic hazard app is available in the App Store

Perhaps most important for the science of probabilistic seismic hazard assessment that is also used in the U.S., and which forms the foundation of the Temblor app, a high chance of shaking at the site of the quakes was forecast in the Japanese national seismic hazard model (warm colors in the map above). Further, both the strike-slip faults that likely ruptured today, and other inclined (dipping) sources along the shore, were known to the Japanese geologists and seismologists, and so were included in the model.

Broadly, these faults are part of the Oita-Kumamoto Tectonic Line (OKTL), which is itself the southern continuation of the Median Tectonic Line (MTL). This 800-km (500-mi) long fault zone is among Japan’s most dangerous inland faults, and plays a tectonic role very similar to the San Andreas fault in California (Mahony et al., 2011) at about half the San Andreas slip rate. The most recent large earthquake on the MTL system was the 1995 Kobe earthquake, about the same size as today’s quake.

The Kobe shock claimed 6,000 lives, whereas a quake of the same size and time in California, the 1989 Loma Prieta quake, took about 60. This humiliating loss utterly changed the practice of seismology in Japan. Almost overnight, seismic networks were transformed from feudal baronies into highly integrated and centralized data collection systems that were opened up to all the world’s scientists for instant sharing and collaboration. Today, just about every facet of the Japanese seismic monitoring systems surpasses all others, and seismologists are attracted to Japan like moths to a light.

Was the M=6.1 a foreshock of the M=7.0, or was the M=7.0 an aftershock of the M=6.1?

So far, the evidence suggests that both are true. Depending on how one counts (and how one counts matters), something like 2-10% of mainshocks are preceded by foreshocks. That’s the good news. The bad news is that no one—no one—can tell a foreshock from any other shock. Foreshocks lack any distinguishing features that mark them for future greatness. So, while tantalizing, this hindsight statistical association has ultimately proved a dead end. But increasingly, we have come to accept that each quake starts a game of roulette: There is a small chance the shock will trigger a big one, and a large chance that it won’t. Earthquakes beget earthquakes, yet most are small, and most triggered quakes are smaller than the triggering quake. But not always. And that brings us back to today’s sequence.

14 Apr 2016 M6 CFF

On April 14, Shinji Toda at Tohoku University calculated the Coulomb stress imparted by the M=6.1 quake to surrounding faults, using the Coulomb 3 software that Shinji, Jian Lin, Volkan Sevilgen and I have developed over the past decade. Shinji generously made the map shown here available to the Japanese press on April 14. His calculation assumes that surrounding faults are right-lateral and roughly parallel to the strike to the M=6.1 shock—reasonable but untested assumptions.

What one sees is startling: Both the Hinagu and Futagawa faults lie in the (red) stress trigger lobes, where we would expect more aftershocks and a heightened chance of a subsequent mainshocks. The extent of the trigger zones, about 35 km, is also roughly the length of the M=7.0 rupture.

Was this an earthquake prediction? Absolutely not. Rather, the calculation shows that the roulette odds got better in the trigger zones, and worse in the (blue) stress shadows. If one earthquake ratchets up the stress on a nearby fault, its more likely to fail. Relieve the stress, and it becomes less likely to fail. It’s not a prediction, but it is progress.

It will be fascinating to see if the 28 hours of small aftershocks of the M=6.1 event lit up the future fault rupture. Based on past published studies and experience by ourselves and others, the answer will probably be no, or at best, sort of. But that’s the state of the science, and the state of the art.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS National Earthquake Information Center, Japan Meteorological Agency (JMA), National Research Institute for Earth Science and Disaster Resilience (NIED); Shinji Toda (IRIDES, Tohoku University); S.H. Mahony, L.M. Wallace, M. Miyoshi, P. Villamor, R.S.J. Sparks and T. Hasenaka (2011), Volcano-tectonic interactions during rapid plate-boundary evolution in the Kyushu region, SW Japan, Geol. Soc. Amer. Bull., 123, doi: 10.1130/B30408.1

You can check your seismic hazard or view aftershocks using Temblor.

Calaveras swarm: Something Learned and Something Lost

A burst of seventeen 1.0≤M≤3.2 earthquake struck 0.2 mi (0.5 km) east of the Calaveras fault trace, east of San José, California, on 29-30 March 2016 at about 5-6 mi (8-10 km) depth. The Temblor seismic hazard rank there is very high (98 out of 100), due largely to the convergence of the active Calaveras and Hayward faults, and to a lesser extent to the San Andreas.

Temblor map of the 29-30 March swarm (red quakes) surrounded by the sites of recent M=5-6 quakes on the Calaveras fault. The adjacent section of the Hayward fault may also have ruptured in 1891.
Temblor map of the 29-30 March swarm (red quakes) surrounded by the sites of recent M=5-6 quakes on the Calaveras fault. The adjacent section of the Hayward fault may also have ruptured in 1891.

The swarm lies near the southern end of the 1911 M=6.6 Calaveras fault earthquake as estimated by Diane Doser et al. (2009) from remote seismic data, and at the likely northern end of the 1984 M=6.2 Morgan Hill earthquake from much more accurate seismic and geodetic data (David Oppenheimer et al., 2010). The swarm also lies 2 mi (3 km) north of the 1984 M=6.2 epicenter. This proximity suggests that there is some kind of irregularity, bend, or break in the Calaveras fault at this location.

At the site of the cluster (the epicenter of the largest shock is shown as a red star), one sees a trough or depression along the fault and a range to the east. The Calaveras strands are orange, a much older fault is blue. We infer that the trough indicates that the fault has a jog or ‘echelon’ at this location: The southern branch perhaps lies on the west side of the trough, and the northern branch lies on the east side. Echelons like this create damage zones—sites of spalling and secondary fractures—that could be the site of the swarm. Google Earth image.
At the site of the cluster (the epicenter of the largest shock is shown as a red star), one sees a trough or depression along the fault and a range to the east. The Calaveras strands are orange, a much older fault is blue. We infer that the trough indicates that the fault has a jog or ‘echelon’ at this location: The southern branch perhaps lies on the west side of the trough, and the northern branch lies on the east side. Echelons like this create damage zones—sites of spalling and secondary fractures—that could be the site of the swarm. Google Earth image.

The Calaveras fault has a slip rate of 15±3 mm/yr in this location, and so the accumulated slip since 1911 is 5 ft (1.5 m), enough to permit another M=6.6 to strike in roughly the same location. Such an event, if it occurred, would strongly shake San José. Nevertheless, repeats of quakes in the same location and of the same size are rare, and so while possible, it is by no means expected.

Essential Data Lost to Science Forever

The 1911 quake, the only M≥6 event in the Bay Area during the 75 years after the great 1906 quake, struck in the ‘stress shadow’ of the 1906 earthquake, which imparted to that portion of the right-lateral Calaveras fault a 5-bar left-lateral stress. We wondered, could the 1911 event have been a ‘retrograde quake,’ in other words, with left-lateral slip on a right-lateral fault, something never before seen? So, our team, which was led by Diane Doser of the University of Texas at El Paso, needed to learn if there were surface rupture, and if so, in what sense; and we needed a seismic focal mechanism that could only be obtained by collecting seismograms in all quadrants, or in as many directions as possible from the epicenter, and as close as possible.

The 1911 earthquake lies in the stress shadow of the 1906 M=7.8 San Andreas earthquake, the lone anomaly to what was otherwise a 75-year period of seismic sleep for the San Francisco Bay area. From Doser et al. (2009).
The 1911 earthquake lies in the stress shadow of the 1906 M=7.8 San Andreas earthquake, the lone anomaly to what was otherwise a 75-year period of seismic sleep for the San Francisco Bay area. From Doser et al. (2009).

A Southern Pacific rail line and a major water main crossed the southern end of the likely rupture, and there was a newspaper report of a broken water pipe. But, the report did not describe how the pipe had broken, and the damage and repair records had since been discarded. The great Lick Observatory opened in 1888 on Mount Hamilton, just 4 mi (7 km) from the likely fault rupture, for which regular geodetic surveys (‘astronomic azimuth’ measurements) would have been needed to align the telescope, but these, too, were gone.

About a dozen U.S. seismic observatories logged the earthquake in their summaries, but we needed copies of the actual smoke-drum seismograms. UC Berkeley had a seismometer at the Lick Observatory, by far the closest. Perry Byerly, Berkeley’s great seismologist, removed the 1911 seismogram from the archive for study, but it was never returned.

(Left) Father James B. Macelwane, S.J. (1883–1956) organized the Jesuit Seismological Service, whose central station is at Saint Louis University. The Macelwane Medal is awarded annually by the American Geophysical Union to its most accomplished young scientists. We owe the lone US recording the 1911 earthquake to Father Macelwane. (Right) Comparison of seismograms for the 1984 Morgan Hill (top) and 1911 Calaveras (bottom) earthquakes recorded on similar seismometers at Debilt, Netherlands. From Doser et al. (2009).
(Left) Father James B. Macelwane, S.J. (1883–1956) organized the Jesuit Seismological Service, whose central station is at Saint Louis University. The Macelwane Medal is awarded annually by the American Geophysical Union to its most accomplished young scientists. We owe the lone US recording the 1911 earthquake to Father Macelwane. (Right) Comparison of seismograms for the 1984 Morgan Hill (top) and 1911 Calaveras (bottom) earthquakes recorded on similar seismometers at Debilt, Netherlands. From Doser et al. (2009).

In the early years of the century, most U.S. seismic observatories were run by scientist-scholar-priests at Jesuit universities. But by the time these professors began to die in mid-century, the universities had lost some of their scientific fervor, and the lifelong seismogram archives of the priests were most often thrown out. John Ebel, Chair of Earth Sciences at Boston College, home of the Weston seismic Observatory, generously helped us try to track the records down. But in the end, only one 1911 seismogram from the U.S., at the University of St. Louis, survived. We ended up relying on one seismograms from Ottawa, and two from Europe, to study a California quake—which proved most compatible with a conventional right-lateral mechanism.

Shameful.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS Calnet and

Doser, Diane I., Kim B. Olsen, Fred F. Pollitz, Ross S. Stein, and Shinji Toda (2009), The 1911 M∼6.6 Calaveras earthquake: Source parameters and the role of static, viscoelastic, and dynamic Coulomb stress changes imparted by the 1906 San Francisco earthquake, Bull.Seismol. Soc. Amer., 99, 1746–1759, doi: 10.1785/0120080305

Oppenheimer, David H., William H. Bakun, Tom Parsons, Robert W. Simpson, John Boatwright, and Robert A. Uhrhammers (2010), The 2007 M5.4 Alum Rock, California, earthquake: Implications for future earthquakes on the central and southern Calaveras Fault, J. Geophys. Res., 115, B08305, doi:10.1029/2009JB006683.

Do you live near the Calaveras fault? Check your home’s seismic risk at http://temblor.net

Pair of magnitude-4 earthquakes lights up one end of a 25-mile-long fault in Oklahoma that could host a larger quake

Temblor Insight|Mar 29, 2016

The M=4.2 shock, and a M=4.1 aftershock 5 hr 26 min later, struck just 45 miles north of Oklahoma City, between the West Lawrie and Sooner Trend oil fields. The M=4.2 shock was felt in Oklahoma City, Tulsa, and Wichita, Kansas. The earthquake depths are shallow, but currently uncertain (4-5 km depth with an uncertainty of about the same extent). The quake location and depth are consistent with being induced by deep reinjection of ‘produced water’ or oil and gas field waste water.

Temblor map of today’s M=4.2 and M=4.1 Crescent, Oklahoma earthquakes, with the Oklahoma Geological Survey fault map (see also McNamara et al, 2015) and the sense of slip on the faults that we infer from the focal mechanism of today’s quake. We consider that slip on the east-west fault is the most likely source of the earthquakes.
Temblor map of today’s M=4.2 and M=4.1 earthquakes, with the Oklahoma Geological Survey fault map (see also McNamara et al, 2015) and the sense of slip on the faults that we infer from the focal mechanism of today’s quake. We consider that slip on the east-west fault is the most likely source of the earthquakes.

The sense of motion (‘focal mechanism’) of the M=4.2 quake suggests either left-lateral slip on the 25-mile (40-km) long east-west fault, or right lateral motion on the north-south fault, with the former more likely based on the earthquake locations (their uncertainty is about ±0.6 mi or 1.1 km). The Oklahoma fault map comes from the Oklahoma Geological Survey (2015); it’s an extension of Holland (2013) and is based on focal mechanisms, which are less certain than a map based on surface mapping. Nevertheless, the inferred 25-mi long east-west fault means there is a possibility of a larger rupture, up to M~6.2. The north-south fault is considerably longer, and cuts through Oklahoma City.

Result of the probabilistic seismic hazard assessment of Peterson et al (2016) shows that the chance of damage in Oklahoma exceeds that of California, Seattle in the Pacific Northwest, and New Madrid in the central U.S
Result of the probabilistic seismic hazard assessment of Petersen et al (2016) shows that the chance of damage in Oklahoma exceeds that of California, Seattle in the Pacific Northwest, and New Madrid in the central U.S

Mark Petersen et al. have just published the first USGS seismic hazard assessment of the ‘oil patch,’ the areas of Oklahoma, Kansas, Texas, Arkansas, and Colorado where induced earthquakes have become common over the past decade. Unlike natural or ‘tectonic’ quakes, the rates of induced earthquakes are highly sensitive to the reinjection volumes and pressures, and so cannot be accurately forecast without knowledge of the realtime injection well activity. So, instead the USGS assessment uses the past 1-2 years of seismicity to make a one-year forecast for 2016. To assess the hazard, one also has to assume an upper earthquake magnitude, which is of course quite uncertain because the record of induced quakes is only about 15 years long. Peterson et al. used M-max = 7.1, which strikes us as reasonable and prudent. The results show the dramatic impact of induced seismicity on hazard and the potential of damage.

Central Oklahoma surpasses California in the annual chance of damage, and has a large region with more than a 1 in 10 chance of damage. Oklahoma City and Dallas also stand out as particularly vulnerable to seismic damage, followed by greater Los Angeles, the San Francisco Bay area, and Seattle in the West, and by New Madrid in the central US, site of several enigmatic M~7 tectonic quakes in 1811-1812 and a high rate of small shocks today.

We will now work to incorporate the new USGS hazard assessment into the Temblor seismic hazard rank and damage estimates, so that people in the oil patch can assess their seismic risk and consider ways to reduce it, including retrofit and insurance.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS; Oklahoma Geological Survey; and Mark D. Petersen, Charles S. Mueller, Morgan P. Moschetti, Susan M. Hoover, Andrea L. Llenos, William L. Ellsworth, Andrew J. Michael, Justin L. Rubinstein, Arthur F. McGarr, and Kenneth S. Rukstales, 2016 One-Year Seismic Hazard Forecast for the Central and Eastern United States from Induced and Natural Earthquakes, U.S. Geol. Surv. Open-File Rep. 2016–1035; and McNamara, D.E., HM Benz, R.B. Herrmann, E.A. Bergman, P. Earle, A. Holland, R. Baldwin, and A. Gassner (2015), Earthquake hypocenters and focal mechanisms in central Oklahoma reveal a complex system of reactivated subsurface strike-slip faulting. Geophys. Res. Lett., 42, 2742–2749. doi: 10.1002/2014GL062730; Austin A. Holland (2013) Optimal fault orientations within Oklahoma, Seismol. Res. Lett., 84, 876-890, doi: 10.1785/0220120153.

Living with Liquefaction

During intense earthquake shaking, water-saturated sediments can turn into a slurry (liquefaction), causing buildings, cars and other heavy objects lying on top of what were formerly stiff, dry sediments or sand, to sink or tilt. This is something I experienced firsthand while pursing my M.Sc. degree in Geology at the University of Canterbury in 2013-2015.

Christchurch and Tohoku transformed our understanding of liquefaction

In the 2011 earthquakes in Christchurch, New Zealand, and Tohoku, Japan, liquefaction was extremely widespread, in some cases, devastating entire neighborhoods. However, an outgrowth of these events is a much better understanding about where liquefaction can happen, when it can happen, and what it can do. In fact, Christchurch residents became some of the most quake-savvy people in the world.

Forget about setting the parking brake; these cars are going nowhere. Christchurch neighborhoods like this one became unrecognizable due to massive liquefaction in 2011. As the water drains after the quake, the slurry congeals into cement, making its removal difficult and expensive. Photo courtesy of Stuff.co.nz
Forget about setting the parking brake; these cars are going nowhere. Christchurch neighborhoods like this one became unrecognizable due to massive liquefaction in 2011. As the water drains after the quake, the slurry congeals into cement, making its removal difficult and expensive. Photo courtesy of Stuff.co.nz

At Temblor, we want to people to better prepare themselves for what could come to pass. Perhaps one reason why earthquakes are not often discussed is fear. The idea of a magnitude-9 Cascadia earthquake off the coast of Oregon and Washington, or a magnitude-8 along the San Andreas Fault scares us all. So, in several blog posts, I will attempt to shed light on what liquefaction is, using my former home of Christchurch, New Zealand as a case study of what it is like to live with and be surrounded by liquefaction.

At 4:35 a.m. on September 4, 2010, Christchurch was rattled by a magnitude-7.1 earthquake. Over the next 4 years, over 10,000 aftershocks of varying size shook the city, most notably a magnitude-6.3 quake on February 22, 2011 which left 185 people dead, and large sections of the city in ruin. The February earthquake was so devastating in part because the epicenter was shallow (5 km or 3 mi) and located a few miles outside the city, meaning urban levels of shaking were some of the highest ever recorded, and the liquefaction was among the most profound and widespread ever experienced. However, Christchurch did not liquefy in every earthquake, and large sections of the city were left nearly unharmed by the earthquakes, making driving through the city an eerie experience. Nevertheless, liquefaction did occur on at least 8 occasions throughout the city. Additionally, in the magnitude-5.7 February 14, 2016 Valentine’s Day Earthquake, Christchurch one again experienced liquefaction. This not only highlighted how long earthquake sequences can last, but brought more damage to the still recovering city.

When liquefaction occurs, structures such as this Christchurch garage can sink and tilt. Photo courtesy of Becker Fraser Photos.
When liquefaction occurs, structures such as this Christchurch garage can sink and tilt. Photo courtesy of Becker Fraser Photos.

Temblor seeks to make it easy to learn where the liquefaction potential is high

In this Temblor map, areas deemed by the USGS to have very high liquefaction susceptibility in northern San Francisco are sites of fill (artificial land); the South of Market (SoMa) area was formerly a marsh and Mission Bay. All suffered liquefaction in the 1906 and 1989 earthquakes.
In this Temblor map, areas deemed by the USGS to have very high liquefaction susceptibility in northern San Francisco are sites of fill (artificial land); the South of Market (SoMa) area was formerly a marsh and Mission Bay. All suffered liquefaction in the 1906 and 1989 earthquakes.
Temblor recently added liquefaction susceptibility maps for all of Oregon and Washington. These maps illustrate how large portions of both cities are susceptible to liquefaction. More Temblor maps of additional areas will be going up shortly.
Temblor recently added liquefaction susceptibility maps for all of Oregon and Washington. These maps illustrate how large portions of Seattle and Portland are susceptible to liquefaction. More Temblor maps of additional areas will be going up shortly.
Houses that tilted and sunk in the 1906 earthquake (Courtesy of the Bancroft Library, U.C. Berkeley)
Houses that tilted and sunk in the 1906 earthquake due to liquefaction (Courtesy of the Bancroft Library, U.C. Berkeley)

In the next blog post, I will delve into some of the science behind liquefaction, including the research I was involved in during my 3 years in Christchurch. If anyone has questions or comments regarding these blogs or would like to be directed towards liquefaction data and/or research, post in the comments below and I will get back to you as soon as possible.

David Jacobson, Researcher, Temblor, Inc.

Data from GNS Science, University of Canterbury, and Witter et al., USGS Open-File Report 2006-1037, Maps of Quaternary Deposits and Liquefaction Susceptibility in the Central San Francisco Bay Region, California (2006).

Magnitude-4.0 earthquake strikes 20 mi east of the magnificent Teton fault near Jackson, Wyoming

26 February 2016  |  Quake Insights

Today’s earthquake was strongly felt in Jackson, WY. It is a strike-slip event with the center of the rupture at a depth of about 14 km (9 mi). It struck in a region that has been seismically active for the past 20 years, with a seismicity alignment that hints at a blind right-lateral fault striking NW-SE, which would be consistent with the focal mechanism of today’s quake.

The 26 February 2016 M=4.0 quake lies in a region of low hazard—about one-eighth of that in the southern San Francisco Bay area, but still much larger than about 85% of the United States, and close to the beautiful Teton fault, which lifted up the Grand Tetons, and formed the meadows and Jenny Lake on its downthrown side.
The 26 February 2016 M=4.0 quake lies in a region of low hazard—about one-eighth of that in the southern San Francisco Bay area, but still much larger than about 85% of the United States, and close to the beautiful Teton fault, which lifted up the Grand Tetons, and formed the meadows and Jenny Lake on its downthrown side.
Google Earth view of the Teton Fault that has lifted up the Grand Tetons, one of the greatest of the US National Parks. The photo is about 35 mi (60 km) wide and North is to the right.
Google Earth view of the Teton Fault that has lifted up the Grand Tetons, one of the greatest of the US National Parks. The photo is about 35 mi (60 km) wide and North is to the right.

The Teton fault is the product of Basin & Range stretching, creating ‘normal’ (tensional) faults. Its spectacular post-glacial scarps are present along the entire  fault trace, and can be seen from the valley floor owing to their large height. The post-glacial (meaning, less than 15,000 year old) fault offset is as much as 100 ft (30 m) along the middle part of the range, but diminishes to the north and south, mimicking the overall height of the Teton ranges. Although quite active in the latest Quaternary, the fault has been seismically quiet in historic time. Its estimated slip rate is 1-5 mm/yr.

Today’s quake struck within a nest of seismicity that has persisted for the past 20 years—near but definitely not on the Teton fault. Source: USGS
Today’s quake struck within a nest of seismicity that has persisted for the past 20 years—near but definitely not on the Teton fault. Source: USGS
One of the most exciting uses of Temblor is to open it in the field, so you can see exactly where the fault scarps have been etched into the landscape. This photo was taken by Temblor developer, Ali Kim, on a backpacking trip last summer. I backpacked into the high country with my daughter there four years ago, where we had a sudden but fortunately safe encounter with a black bear.
One of the most exciting uses of Temblor is to open it in the field, so you can see exactly where the fault scarps have been etched into the landscape. This photo was taken by Temblor developer, Ali Kim, on a backpacking trip last summer. I backpacked into the high country with my daughter there four years ago, where we had a sudden but fortunately safe encounter with a black bear.

Ross Stein & Volkan Sevilgen, Temblor, Inc.

Data: University of Utah Seismographic Stations, USGS Jackson Hole Seismic Network;  Hampel, A., Hetzel, R., Densmore, A.L., 2007, Postglacial slip-rate increase on the Teton normal fault, northern Basin and Range Province…, Geology, 35, doi: 10.1130/G24093A.1; Byrd, J.O.D., Smith, Robert B., and Geissman, John W., 1994, The Teton fault, Wyoming—Topographic signature, neotectonics, and mechanisms of deformation: J. Geophys. Res., 99, no. B10, p. 20,095–20,122.

You can check your seismic risk at temblor.net

Magnitude-5.7 Valentine’s Day Earthquake Brings Canterbury Earthquake Sequence Back to Life

Quake Insight | Feb 22, 2016

Over 5 years since the Canterbury Earthquake Sequence started, the city of Christchurch is still being rattled by large aftershocks.

The magnitude 5.7 earthquake, which was centered 15 km east of Christchurch, at a depth of 15 km, not only brought more damage, but memories of nearly five years ago when a deadly quake shook the city. This most recent event, which was located offshore in the Pacific Ocean, was felt to varying degree throughout New Zealand’s South Island. It was also the largest earthquake in the area since a magnitude 5.9 on December 23, 2011, which had a similar epicenter. Based on this data, the earthquake likely involved slip on an oblique thrust fault, and means the earthquake sequence which began in September 2010 is still ongoing.

This diagram highlights not only location of the February 14th earthquake, but faults distributed around the Canterbury region. Image from Stuff.co.nz.
This diagram highlights not only location of the February 14th earthquake, but faults distributed around the Canterbury region. Image from Stuff.co.nz.

Distribution of Damage and Degree of Shaking Highlights Earthquake Complexity

While the magnitude of this earthquake was not as large as some that have hit the region, because the epicenter was shallow, intense shaking was felt, and the city experienced more damage and liquefaction. The iconic Christchurch Cathedral, which was severely damaged in 2011, and is undergoing demolition, lost more of its façade, and eastern suburbs once again had to deal with liquefaction. Additionally, cliffs collapsed along the coast, creating large dust clouds, and forcing people to run for shelter. For some residents in the area, including friends of mine, every shake brought down more rocks which was unnerving.

Dust clouds formed after large cliffs collapsed in the coastal community of Sumner following the magnitude-5.7 earthquake. Photo by Graeme Jolliffe
Dust clouds formed after large cliffs collapsed in the coastal community of Sumner following the magnitude 5.7 earthquake. Photo by Graeme Jolliffe

The recurrent liquefaction in the eastern suburbs highlights how certain areas can be much more prone to certain geologic hazards. Though more detail will be explained in a series of Temblor blog posts titled “Living with Liquefaction” much of this susceptibility can be attributed to near-surface geology. Even subtle differences in sediment coarseness can significantly impact whether or not liquefaction will occur. For example, in some neighborhoods in Christchurch, houses are built on ancient dune sand, while others are on more modern silty river channels. In this instance, the river channel deposits would be more prone to liquefaction. This varying geology, sometimes separated by only feet, is one of the reasons why liquefaction can be so variable.

Once again, cleanup of liquefaction had to be done in many of Christchurch’s eastern suburbs. In some cases, streets resealed only days prior, for the first time since the February 2011 earthquake were once again destroyed. However, in true kiwi fashion everyone came and helped out. Photo by Iain McGregor.
Once again, cleanup of liquefaction had to be done in many of Christchurch’s eastern suburbs. In some cases, streets resealed only days prior, for the first time since the February 2011 earthquake were once again destroyed. However, in true kiwi fashion everyone came and helped out. Photo by Iain McGregor.

Just as liquefaction was site-specific so was shaking. Though shaking was deemed “severe” by GNS Science, through both talking to people and reading reports, the way in which it was felt varied significantly throughout the city. Some say there was a bang, followed by a bit of rolling, while others say it lasted for about 20 seconds with rolling only getting stronger and stronger.

Having both experienced and studied earthquakes in Christchurch, it seems safe to say that the same near-surface geology which impacted where liquefaction occurred, also influenced the way shaking was felt. In fact, the two are related. In areas where liquefaction was present, rolling likely dominated and lasted for longer periods of time, due to shallow water tables and near-surface silty deposits. Such a combination could prolong the rolling and feel as if you were sitting on a waterbed. While not exactly this cut-and dry, there is a definite relationship between near-surface geology, and the shaking experienced during an earthquake.

Looking Forward

Following this most recent event, residents of the Garden City had memories of the deadly February 22, 2011 earthquake brought back to the forefront. However, what it also did was illustrate that an earthquake sequence can last for extended periods of time. Even though this sequence started over 5 years ago, large earthquakes still occur, and GNS Science estimates that there is a 63% chance (Up from 49%) of another magnitude 5.0-5.9 earthquake occurring in the next 12 months. Because of this, it seems right to say to the city of Christchurch “Kia Kaha,” a Māori phrase meaning “stay strong” which became iconic following the February 2011 earthquake.

David Jacobson, Researcher, Temblor, Inc. 

Sources Include: GNS Science, Stuff.co.nz, One News New Zealand, Recurrent liquefaction in Christchurch, New Zealand during the Canterbury earthquake sequence, Geology 41 (4) p. 419-422, Bastin, S., Quigley, M.C., Bassett, K. (2015) Comparison of liquefaction-induced land damage and geomorphic variability in Avonside, New Zealand, 6th International Conference on Earthquake Geotechnical Engineering, 1-4 November 2015, Christchurch, New Zealand

Magnitude-4.8 shock near Big Pine, CA, strikes just north the 1872 M=7.6 Owens Valley quake, recalling the contemporary account of naturalist John Muir

16 February 2016  |  Quake Insights

The M=4.8 Big Pine, CA quake was followed by a M=4.2 aftershock and several smaller ones; both are right-lateral ruptures at a depth of about 15 km (9 mi). They struck in a very active belt of the ‘Walker Lane’ active faults and volcanic features.

Temblor map of today’s M=4.8 mainshock and several aftershocks. The northern end of the 100-km-long (60 mi) 1872 M=7.6 Owens Valley rupture extends through the ‘g’ of Big Pine.
Temblor map of today’s M=4.8 mainshock and several aftershocks. The northern end of the 100-km-long (60 mi) 1872 M=7.6 Owens Valley rupture extends through the ‘g’ of Big Pine.

The 1872 M=7.6 Owens Valley earthquake is the third largest shock to strike California since reliable accounts began in about 1800, exceeded only by the 1857 M=7.9 and 1906 M=7.7 shocks on the southern and northern San Andreas faults respectively. Although the magnitudes of pre-instrumental quakes are uncertain, the surface slip and rupture length was carefully mapped by Lubetkin (1988) and Beanland and Clark (1994), and so only it’s depth extent is uncertain. As a result, few doubt that this was the third largest California quake.

The Walker Lane belt is perhaps the eastern periphery of the North American-Pacific plate boundary shear zone, of which the San Andreas is the most prominent feature. The belt accommodates right-lateral shear, but there also extension aligned roughly northeast-southwest. This extension gives rise to the ‘normal’ (extensional) faults that form the eastern margin of the Sierra Nevada (snow covered rocks in the lower left), and also to active magmatic cones (the dark brown conical features in the center bottom) that are cut and right-laterally offset by the Owens Valley fault.
The Walker Lane belt is perhaps the eastern periphery of the North American-Pacific plate boundary shear zone, of which the San Andreas is the most prominent feature. The belt accommodates right-lateral shear, but there also extension aligned roughly northeast-southwest. This extension gives rise to the ‘normal’ (extensional) faults that form the eastern margin of the Sierra Nevada (snow covered rocks in the lower left), and also to active magmatic cones (the dark brown conical features in the center bottom) that are cut and right-laterally offset by the Owens Valley fault. (Temblor Map)

Right-lateral slip on the Owens Valley fault during the past 20,000 years is 1-4 mm/yr, according to Beanland and Clark, 1994 and Lubetkin, 1988, or about a tenth of that on the San Andreas. So great shocks on the fault must be much less frequent, but no less damaging, than on the San Andreas. The 1872 earthquake produced right-lateral offsets averaging about 6 m (20 ft) along the 100 km fault length, according to Beanland and Clark (1994).

In this Google Earth image, North is oriented to the lower right. The diagonal is about 100 km (60 mi). The 1872 M=7.6 rupture is red, whereas the normal faults bounding the Sierra Nevada are yellow (if active in the past 20,000 yrs) and blue (if active only sometime during the past 2 million years).
In this Google Earth image, North is oriented to the lower right. The diagonal is about 100 km (60 mi). The 1872 M=7.6 rupture is red, whereas the normal faults bounding the Sierra Nevada are yellow (if active in the past 20,000 yrs) and blue (if active only sometime during the past 2 million years).

The great John Muir, founder of the Sierra Club, and champion and defender of Yosemite, was camped in Yosemite Valley at the time of the 1872 quake, and witnessed massive rockfalls in response to the shaking. Beautifully capturing the excitement we all feel when the earth reveals her dynamism to us, he wrote in his journal,

“…though I had never before enjoyed a storm of this sort, the strange, wild thrilling motion and rumbling could not be mistaken, and I ran out of my cabin, near the Sentinel Rock, both glad and frightened, shouting, ‘A noble earthquake!’ feeling sure I was going to learn something. The shocks were so violent and varied, and succeeded one another so closely, one had to balance in walking as if on the deck of a ship among the waves, and it seemed impossible the high cliffs should escape being shattered.”

Ross Stein and Volkan Sevilgen

Data from USGS, California Geological Survey; Sarah Beanland and Malcolm Clark (1994), The Owens Valley fault zone, eastern California, and surface rupture associated with the 1872 earthquake, U.S. Geol. Surv. Bull., 1982, 1–29; Lester Lubetkin (1988), Late Quaternary activity along the Lone Pine Fault, eastern California, Geol. Soc. Am. Bull., 100, 755–766; Steven G. Wesnousky (2005), Active Tectonics of the Walker Lane, Tectonics, 24, doi:10.1029/2004TC001645.

Could a great quake strike on the enigmatic San Jacinto fault?

Today’s magnitude-3.5 Moreno Valley, CA, quake near the San Jacinto fault begs the question

The 13.5 km (8 mi) deep right-lateral strike-slip earthquake was widely, though weakly, felt in the cities of Riverside, Redlands, San Bernardino, Hemet and Corona. The event struck on or close to the San Jacinto fault, with a slip rate of about 12 mm/yr (0.5 in/yr) is one of California’s most active faults, and so the seismic hazard rank at this location is high. The same or adjacent section of the fault experienced a M=6.8 shock in 1918. Since that time, the section has accumulated a ‘slip deficit’ of about 1.2 m (4 ft), and so another M~6.8 shock is certainly possible in the near future. But what about larger shocks?

The highly active San Jacinto faults splits off the San Andreas fault near San Bernardino. The San Jacinto is composed of a series of 30-mi long sections, each offset from the next. Could the entire fault rupture all at once?
The highly active San Jacinto faults splits off the San Andreas fault near San Bernardino. The San Jacinto is composed of a series of 30-mi long sections, each offset from the next. Could the entire fault rupture all at once?

The San Jacinto fault extends southeast from the San Andreas fault, making it difficult to distinguish the slip rate of the San Jacinto from the adjacent section of the San Andreas. But the most recent geologic and geodetic evidence suggests that the San Andreas probably slips at almost twice the rate, at about 21 mm/yr, and so has a doubled rate of moderate to large shocks.

The San Jacinto fault is etched into the landscape in this Google Earth image. The fault is the yellow line running from the upper left to the lower right.
The San Jacinto fault is etched into the landscape in this Google Earth image. The fault is the yellow line running from the upper left to the lower right.

During the past 120 years of historical and instrumental records, no earthquake larger than magnitude-6.8 has struck along any part of the San Jacinto fault, raising the possibility that its maximum magnitude could be capped at about M~7 despite its 135 mi (200 km) length, which would otherwise make magnitude of M~7.5 possible. Bear in mind that this difference is important: A M=7.5 shock is twenty times larger than the M=6.8 in 1918, and a million times larger than today’s M=3.5 quake.

Magnitude 3.5 earthquake felt widely (blue-purple squares)
Magnitude 3.5 earthquake felt widely (blue-purple squares)

But the San Jacinto is unique in its ‘en echelon’ character. Rather than a continuous fault like most of the San Andreas, the San Jacinto is broken up into a series of ~30 km (20 mi) long sections offset from each other (referred to as ‘echelons’) by as much as 5 km (3 mi). These offsets, if they extend to depth, may prevent—or at least inhibit—a rupture from jumping from one section to another, which would be needed to create a M>7 rupture. Today’s quake struck at the northernmost end of one of these echelons.

While one might dismiss the possibility of a great rupture, in 1992 a series of echelon faults ruptured together to create the powerful M=7.3 Landers, CA, earthquake. Humbled by this surprise, one should not assume that the past century of seismic behavior will represent the next. Recent work by Salisbury et al. (2012) suggests that prehistoric earthquakes along the fault produced slip of up to 4 m (13 ft), which would require M~7.5 earthquakes. They also uncovered a poorly located large earthquake occurred in southern California on 22 November 1800 that might have been a M>7 shock on the San Jacinto fault.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Caltech/Southern California Seismic Network; and  J. B. Salisbury, T. K. Rockwell, T. J. Middleton, and K. W. Hudnut, ‘LiDAR and Field Observations of Slip Distribution for the Most Recent Surface Ruptures along the Central San Jacinto Fault’, Bull. Seismol. Soc. Amer., 102, doi: 10.1785/0120110068 (2012); and Thomas Rockwell, Christopher Loughman, and Paul Merifield, ‘Late Quaternary rate of slip along the San Jacinto Fault Zone near Anza, southern California,’ J. Geophys. Res., doi: 10.1029/JB095iB06p08593 (1990).

Check your own seismic risk at temblor.net

Magnitude-5.1 northern Oklahoma quake produces aftershocks over a surprisingly broad 5 by 8 mi area

 13 February 2016  | Revised Quake Insights

The foreshock has been removed from the catalog, so perhaps this was a phantom event.

Five hours after the mainshock, improved earthquake depths and locations, as well as five aftershocks, have altered and enhanced the picture of what is likely induced seismic burst associated with deep injection of produced water.

Today’s M=5.1 quake has been followed by 6 aftershocks (red) in 5 hours over a wide area. It is possible that some are unrelated to the mainshock. The dashed left-lateral fault is our interpretation.
Today’s M=5.1 quake has been followed by 6 aftershocks (red) in 5 hours over a wide area. It is possible that some are unrelated to the mainshock. The dashed left-lateral fault is our interpretation.

The various depth determinations of the mainshock are now consistently about 8 km (5 mi), substantially deeper the bottom of any re-injection well. This would mean that fluids would need to migrate downward under injection pressures to trigger the mainshock. In addition, a M=3.9 aftershock now locates to the southeast of the mainshock, along a trend of quakes that struck during the preceding month. The relative location of the largest events, combined with the focal mechanism, might suggest a northwest-striking right-lateral fault with a length of at least 6 km and a width (the down-dip dimension) of at least 8 km. Such a fault is capable, in principle, of hosting a M=6.0 earthquake.

The quake was felt throughout almost all of Oklahoma and much of southern Kansas, although the shaking was light. Strongest shaking was reported by the USGS Did You Feel It? close to the epicenter, which lies midway between the towns of Woodward and Enid, but the epicenter was fortunately far from urban centers.
The quake was felt throughout almost all of Oklahoma and much of southern Kansas, although the shaking was light. Strongest shaking was reported by the USGS Did You Feel It? close to the epicenter, which lies midway between the towns of Woodward and Enid, but the epicenter was fortunately far from urban centers.

The largest quake to strike Oklahoma since 1980 is a M=5.6 shock 60 km (40 mi) east of Oklahoma City on 5 November 2011.

Ross Stein and Volkan Sevilgen

Data from USGS, and Oklahoma Geological Survey

Check the aftershocks at Temblor App

Terremoto en Taiwan, Febrero 05, 2016

Febrero 10, 2016

Con el reciente terremoto ocurrido en Taiwan (Febrero 5,2016; 6.4Mw, de acuerdo al USGS), algunas cosas interesantes pueden ser escritas. Hasta ahora los reportes oficiales indican el numero de victimas fatales en 18, lo cual es relativamente poco, considerando la gran destruccion mostrada en los medios de comunicacion, y redes sociales. Quizas el numero de muertos se incremente, pero de seguro que no sera tan catastrofico como el terremoto ocurrido en el centro de dicho pais en 1999 (magnitud 7.6Mw, 2400 personas muertas, ver USGS). Mas recientemente en 2013, otro terremoto en la misma región dejó un total de 4 muertos. Los daños asociados a este terremoto estuvieron relacionados principalmente con problemas geotecnicos, especificamente deslizamientos. La razon quizas podria deberse a la poca profundidad a la que se localizo el epicentro (10 Km).

A pesar de que en el caso del terremoto de Febrero 2016, la profundidad fue un poco mayor (23 Km), al parecer la zona cerca del epicentro consiste de suelos blandos, sobre todo donde se ubica la ciudad mas importante, Tainan, en la que la que los edificios altos fueron los mas afectados. Ademas de aquellos con periodos de vibracion bastante largo, como las estructuras de madera, verdaderas joyas de historia, tipicas de esta region.

Caracteristicas del terremoto

Localizacion: 22.871 °N 120.668 °E (al sur de la isla)
Profundidad: 23.0 Km (14.3 mi)
Hora: 19:57:27 (UTC)
Origen: Choque de placas tectonicas
Magnitud: 6.4 Mw
Shaking expected for a simplified model of the 2016 M=6.3 earthquake (magenta star)  by Dr. Shiann-Jong Lee suggests very strong amplification at large distances from the mainshock, with values of almost 1.0 g in Tainan, and 0.3 g in Taitung and Kaohsiung (Abbreviations: PGA = Peak Ground Acceleration, 980 gal = 1.0 g)
Shaking expected for a simplified model of the 2016 M=6.3 earthquake (magenta star)  by Dr. Shiann-Jong Lee suggests very strong amplification at large distances from the mainshock, with values of almost 1.0 g in Tainan, and 0.3 g in Taitung and Kaohsiung
(Abbreviations: PGA = Peak Ground Acceleration, 980 gal = 1.0 g)
Este modelo de suelo, elaborado por el Dr. Shiann-Jong Lee, para un modelo simplificado del terremoto de Febrero 05, 2016 (indicado con la estrella magenta), sugiera un gran amplificacion sismica, inclusive a distancias grandes, con respecto al epicentro del terremoto. Aunque en lo general, las amplificaciones mostradas no son tan exageradas como otros terremotos, aunque en los alrededores de Tainan al parecer alcanza 1g de aceleracion (Fuente: Temblor.net). De acuerdo al analisis de mecanismos focales presentado en el reporte inicial del USGS y del IRS, la ruptura de falla asociada al evento principal, tiene direccion noroeste-sureste. Segun algunos reportes de blog especializados como temblor.net, indican que la falla donde se genero el sismo es de tipo ciega, es decir no aflora a la superficie y es practicamente oculta a los investigadores. Segun se estima la falla esta localizada a 20 Km de profundidad, y habria que esperar las investigaciones posteriores si la ruptura se extendio hasta la superficie. Lo que si se evidencio es la existencia de las mismas. Aunque hasta ahora no se ha estudiado totalmente este tipo de fallas, algunos estudios realizados en California, indican que este tipo de falla, aunque no son muy grandes pueden generar sismos hasta de magnitudes superiores a los 7.5Mw.
Falla de empuje oculto dentro de la superficie de la corteza (Fuente: Temblor.net)
Falla de empuje oculto dentro de la superficie de la corteza (Fuente: Temblor.net)
En los ultimos 100 años, en Taiwan, se han registrado varios eventos sismicos de considerable magnitud, los cuales en su mayoria han ocurrido dentro de los 200 Km de radio con respecto al epicentro del mas reciente terremoto. Algunos de los eventos han ocurrido debajo de la isla, los cuales han sido de lejos los mas destructivos, comparados con aquellos localizados en la zona de subduccion al norte de la isla. Aqui algunos de ellos (con distancia de referencia con respecto al terremoto de Febrero 05, 2016:
  • Julio 1998; magnitud 5.7Mw; 5 victimas fatales (70 Km al Norte)
  • Diciembre 2006; magnitud 7.0Mw; 2 victimas fatales (120 Km al Sur)
  • Septiembre 1999; magnitud 7.6Mw; 2500 muertos, gran cantidad de daños, tambien conocido por los nombre Chi-chi, o Jiji o 921. Este terremoto es considerado el segundo mas letal en la historia de Taiwan (100 Km al Noroeste)
  • Abril 1935; 3200 muertos. Es el terremoto mas letal en la historia del pais (ligeramente al norte)
  • Diciembre 1941; cientos de muertos (55 Km al Noroeste)
Desde el punto de vista sismotectonico, Taiwan se encuentra localizado, practicamente en el borde de la placa de Filipina, la cual a su vez esta rodeada por las placas del Pacifico, Australiana, Norteamericana y Placa Euroasiatica, verdaderos mostruos en forma de bloques que determinan la sismicidad y el vulcanismo de la region. Terremotos y volcanes son propios de la naturaleza de la zona, desde las islas aleutianas al norte de Japon, las islas del archipielago japones, Indonesia, Filipinas, China, Nepal, Pakistan y Taiwan. Ejemplo de lo maestuoso de lo que ocurre en la region son los grandes eventos acaecidos a lo largo de la historia (9Mw, en Japon, 2011; 9.1Mw, en Indonesia, 2004; el historico volcan Kratatoa; el hecho de la existencia de la cordillera del Himalaya). Asi que, la zona es es de una configuración tectónica sumamente compleja, y continuamente ocurren sismos de considerables magnitudes. Lo que implica que la sociedad misma, de alguna forma está “preparada”, y los códigos de construcción son bastante exigentes. Taiwan, un país con una infraestructura relativamente joven, y por ende de buena calidad. Muchas lecciones serán aprendidas de este terremoto, para ser aplicadas en nuevos códigos sísmicos y en la elaboración de protocolos de medidas de prevencion y mitigación.

Delvin A. Martínez Hokkaido University, Japan

Magnitude-6.3 earthquake near Tainan, Taiwan, highlights the danger of blind thrust faults around the world

6 February 2016  |  Quake Insight  |  Revised

The 5 Feb 2016 M=6.3 event struck at a depth of 20 km (12 mi) about 40 km (25 mi) east of the southern city of Tainan, with a population of 1.9 million. The earthquake was felt throughout Taiwan, and strongly shaking Tainan. A 17-story, 100-unit apartment building constructed before the strengthened building codes were imposed after the 1999 M=7.6 Chi-Chi quake, collapsed, as well as several other buildings. 

Infant rescued from a collapsed 17-story apartment building in Tainan on 6 Feb 2016 (Reuters) http://www.reuters.com/article/us-quake-taiwan-idUSKCN0VE2EO
Infant rescued from a collapsed 17-story apartment building in Tainan on 6 Feb 2016 (Reuters) http://www.reuters.com/article/us-quake-taiwan-idUSKCN0VE2EO

Based on the focal mechanism, aftershocks, geology, and the distribution of shaking, the earthquake most likely involves slip on a blind thrust fault, so none of the major surface-cutting faults would appear to be involved. The most famous blind thrust events in California are the 1983 M=6.7 Coalinga, and 1994 M=6.7 Northridge, shocks. The Taiwan event is very similar in size, location, style, and shaking as the M=6.4 Jiashian earthquake in 2010; the two appear to abut, and so are almost certainly related.

Shaking expected for a simplified model of the 2016 M=6.3 earthquake (magenta star)  by Dr. Shiann-Jong Lee suggests very strong amplification at large distances from the mainshock, with values of almost 1.0 g in Tainan, and 0.3 g in Taitung and Kaohsiung (Abbreviations: PGA = Peak Ground Acceleration, 980 gal = 1.0 g)
Shaking expected for a simplified model of the 2016 M=6.3 earthquake (magenta star)  by Dr. Shiann-Jong Lee suggests very strong amplification at large distances from the mainshock, with values of almost 1.0 g in Tainan, and 0.3 g in Taitung and Kaohsiung
(Abbreviations: PGA = Peak Ground Acceleration, 980 gal = 1.0 g)

taiwan-3

A ‘blind thrust fault’ is one that does not cut the earth’s surface, and therefore is ‘blind’ to geologists. The fault (red at left) causes the overlying strata to be uplifted and warped into a fold, and so blind thrusts are often inferred from surface folds. Blind thrusts can produce M<7.5 quakes, and are a threat in southern and central California.

A slip model by Ching et al (2011) for the 2010 quake colored squares) shows slip on a blind thrust fault. This is a large area and a small slip for a M=6.3 shock, and so perhaps the actual rupture was more compact. Nevertheless, the 2016 M=6.3 shock strikes at the periphery of the 2010 rupture, which was likely brought closer to failure.
A slip model by Ching et al (2011) for the 2010 quake colored squares) shows slip on a blind thrust fault. This is a large area and a small slip for a M=6.3 shock, and so perhaps the actual rupture was more compact. Nevertheless, the 2016 M=6.3 shock strikes at the periphery of the 2010 rupture, which was likely brought closer to failure.

One can see the site of the 2010 M=6.4 shock in the same figure (from H. H. Huang, Y.-M. Wu, T.-L. Lin, W.-A. Chao, J. B. H. Shyu, C.-H. Han, and C.-H. Chang, TAO, 2011), with its approximate rupture area based on the extent of its aftershocks. The mainshocks are only 15 km (9 mi) apart, with the 2016 mainshock on the edge of the 2010 rupture, suggesting that the 2010 shock brought the site of the 2016 rupture closer to failure.

Here, Ching et al (2011) calculated the stress imparted by the 2010 quake to surrounding faults, also known as ‘receiver faults,’ because they receive the stress. The left panel is for thrust receivers striking NE, as in the Chishan fault (CHN); the right panel is for left lateral-thrust faults striking N-S, as in the Chaochou fault (CCU). So, the 2010 quake could have brought the site of the 2016 quake as much as 0.5 bar closer to failure, which is significant if it proves correct. 
Here, Ching et al (2011) calculated the stress imparted by the 2010 quake to surrounding faults, also known as ‘receiver faults,’ because they receive the stress. The left panel is for thrust receivers striking NE, as in the Chishan fault (CHN); the right panel is for left lateral-thrust faults striking N-S, as in the Chaochou fault (CCU). So, the 2010 quake could have brought the site of the 2016 quake as much as 0.5 bar closer to failure, which is significant if it proves correct.
In this cross-section, W is on the left and E is on the right. The topography is in green at top, and the seismic wave speed, Vp, is at bottom Francis T. Wu. The 6 Feb 2016 (Taiwan time) M=6.4 mainshock is the green ‘beach ball’ (focal mechanism). Taiwanese seismologists suspect that the rupture aligns with the small red beachballs on a gently inclined ‘blind’ thrust fault.
In this cross-section, W is on the left and E is on the right. The topography is in green at top, and the seismic wave speed, Vp, is at bottom Francis T. Wu. The 6 Feb 2016 (Taiwan time) M=6.4 mainshock is the green ‘beach ball’ (focal mechanism). Taiwanese seismologists suspect that the rupture aligns with the small red beachballs on a gently inclined ‘blind’ thrust fault.

 

The 4 March 2010 M=6.4 Jiashian earthquake shows a location and rupture style similar to the 6 February 2016 quake (left). The distribution of shaking is also very similar (right). From Huang et al., (2011).
The 4 March 2010 M=6.4 Jiashian earthquake shows a location and rupture style similar to the 6 February 2016 quake (left). The distribution of shaking is also very similar (right). From Huang et al., (2011).
The Chaochou fault marks the razor-sharp boundary between the Central Ranges at the top of this oblique Google Earth image from the Pingtung Plain in the center. Because the fault is almost 100 km (60 mi) long, it is likely capable of a M=7.2 earthquake. The image is oriented with North to the upper left. The city of Tainan is in the lower left. The fault was elucidated in the landmark study of J. Bruce H. Shyu, Kerry Sieh, Yue-Gau Chen, and Char-Shine Liu, ‘Neotectonic architecture of Taiwan and its implications for future large earthquakes,’ J. Geophys. Res., doi:10.1029/2004JB003251 (2005).
The Chaochou fault marks the razor-sharp boundary between the Central Ranges at the top of this oblique Google Earth image from the Pingtung Plain in the center. Because the fault is almost 100 km (60 mi) long, it is likely capable of a M=7.2 earthquake. The image is oriented with North to the upper left. The city of Tainan is in the lower left. The fault was elucidated in the landmark study of J. Bruce H. Shyu, Kerry Sieh, Yue-Gau Chen, and Char-Shine Liu, ‘Neotectonic architecture of Taiwan and its implications for future large earthquakes,’ J. Geophys. Res., doi:10.1029/2004JB003251 (2005).

Today’s earthquake presages modifications to the seismic hazard map for Taiwan now  underway by the Taiwan Earthquake Model group (TEM), an interdisciplinary community of earth scientists and engineers drawn from academia and industry. TEM is using the state-of-the-art open source modeling tool, Open Quake, developed by the Global Earthquake Model (GEM Foundation). TEM not only uses GEM’s tools, but has been a leading contributor to GEM science. Crucially, the TEM geologists have found new faults, re-evaluated older ones, and reassessed the amplification of seismic waves in the basins along western Taiwan.

One can see that the hazard in Tainan in the TEM map is much higher than in the preceding national map developed by the Central Geological Survey. The TEM map is preliminary, and no map or hazard model can forecast earthquake occurrence, and so the M=6.3 quake does not allow one to assess which model is best. But because the new model doubles the hazard in Tainan, and raises the hazard slightly at the M=6.3 epicenter, the 6 February 2016 earthquake lends support to its fidelity and utility. 

Comparison of the active fault map (left) and probabilistic hazard model (center) of Taiwan proposed by the Taiwan Earthquake Model Group, and that by the Central Geological Survey (right), with the site of the M=6.3 earthquake marked.
Comparison of the active fault map (left) and probabilistic hazard model (center) of Taiwan proposed by the Taiwan Earthquake Model Group, and that by the Central Geological Survey (right), with the site of the M=6.3 earthquake marked.

Ross Stein and Volkan Sevilgen, Temblor

Data and acknowledgements: We are very grateful to Prof. Kuo Fong Ma (National Central University) for providing a wealth of preliminary findings. Data is from Taiwan Central Weather Bureau, Taiwan Earthquake Model, Taiwan Earthquake Research Center, Shyu et al. (2005), Huang et al. (2011), Ching et al. (2011), Dr. Shiann-Jong Lee (Academia Sinica), Prof. F. T. Wu (SUNY Binghamton), and Prof. Shinji Toda (Tohoku University), with translation of Taiwanese data by Dr. Jian Lin (Woods Hole Oceanographic Institution).

Show my seismic risk for free at Temblor.net

What would you do if a Japanese tsunami boat washed ashore? Students transform a tragedy into a homecoming

I attended the January meeting of the California Seismic Safety Commission, which looks out for the needs of Californians to prepare for quakes, to be resilient to their effects, and to recover as rapidly as possible afterwards. We have the Commission to thank for earthquake hazards disclosure in home sales, for regulations to retrofit collapse-prone unreinforced masonry buildings, for the California Earthquake Authority that provides residential quake insurance, and for the Pacific Earthquake Engineering Research Institute to learn how to make buildings safer and stronger. There Dr. Lori Dengler from Humboldt State University told the Commissioners one of the most moving stories of loss and healing I have heard in a long time, and so I have to share it.

A painting of the Kamome tsunami boat’s arrival on the shore near Crescent City, CA, in April 2013.
A painting of Kamome’s arrival on the shore near Crescent City, CA, in April 2013.

Takata High School, in the Tohoku fishing city of Rikuzentaka, owned a boat used to teach students about fishing and ship repair. The boat was tied to a platform on a wharf when the 2011 tsunami struck.  No one was using the boat at the time, but the tsunami devastated Rikuzentakata, taking lives, destroying much of the school buildings, and tearing the boat from it’s mooring lines. The boat, along with so much other debris, vanished out to sea.

A painting of the Kamome tsunami boat’s cleaning by Del Norte High School Students
A painting of Kamome’s cleaning by Del Norte High School Students

Two years later, an overturned barnacle-encrusted hull washed ashore near Crescent City, California, 4,000 nautical miles from Rikuzentaka. After scraping off the barnacles from its gunwhale, Lori and others saw the kanji characters. A Japanese speaker translated them as, ‘Kamome (Seagull), Takata High School.’ Remarkably, Lori had visited Rikuzentakata two years beforehand to study the tsunami devastation, and admiring the pluck and spirit of the area, she had ‘liked’ the city’s Facebook page to follow the recovery process.

Now, she had something to tell them: The boat from one of the most tsunami vulnerable fishing towns in Japan had beached at Crescent City, one of the most tsunami vulnerable fishing towns on west coast of the United States. Crescent City had been battered by the tsunami from the 1964 M=9.2 Anchorage, Alaska quake, and also, ironically, by the tsunami from the 2011 M=9.0 Tohoku earthquake itself.

And then things really got interesting. The Del Norte High School students asked the students of Takata High School if they would like their boat back. The answer came roaring back: Yes. The Del Norte High School students cleaned and refurbish the boat, saving the lone remnant of its stern line still cleated to the hull. The students put a YouTube video up asking for the considerable funds needed to ship the boat home, the money came tumbling in, and the boat was returned to the astonished and thrilled school children: Their boat had come home. Not everything lost on 11 March 2011 was lost forever.

But the story does not stop there. The Japanese students invited the Californian students to visit, so they could thank them personally. None spoke Japanese or had ever been out of the country, so they were anxious but excited. When they came, they learned how to enjoy and prepare Japanese food, how to write their names in Japanese characters, and saw their lives mirrored by their new friends in Japan.

Takata High School students try to get their arms around a giant Sequoia
Takata High School students try to get their arms around a giant Sequoia

The departing Americans invited the Takata students to visit them next year in Crescent City. Nervous about speaking English and eating American food, they nevertheless came, fell for hamburgers, sang American songs, learned new games, and saw their first giant Redwood. The students have vowed to remain friends. In two weeks, eight more Del Norte High School students will be traveling to Japan to visit Takata High School, the next remarkable step in the long link formed by a small boat.

On 26 November 2014, Futoshi Toba, Mayor of Rikuzentakata, presented U.S. Ambassador Caroline Kennedy with the saved remnant of Kamome’s stern line, which is now on display at the U.S. Embassy in Tokyo. Also in 2014, Kamome was installed in the National Tokyo Museum as part of a special exhibit on the 2011 tsunami and recovery.
On 26 November 2014, Futoshi Toba, Mayor of Rikuzentakata, presented U.S. Ambassador Caroline Kennedy with the saved remnant of Kamome’s stern line, which is now on display at the U.S. Embassy in Tokyo. Also in 2014, Kamome was installed in the National Tokyo Museum as part of a special exhibit on the 2011 tsunami and recovery.

How could something that grew out of such an immense and unforeseen tragedy confer so much hope and healing? The mirror image communities of Rikuzentaka and Crescent City have much to do with it, as do the Japanese and American high school students themselves. But as a scientist, I also feel that the connection Lori made with the school long before the boat washed ashore is just as important. It’s a reminder that scientific research can be deeper than data, and more powerful than a tsunami, when we let it.

Ross Stein, Temblor

Illustrations and photographs reproduced here with permission from the authors

The bilingual book is “The Extraordinary Voyage of Kamome: A Tsunami Boat Comes Home,” by Lori Dengler, Amya Miller, and Amy Uyeki (Humboldt State Univ. Press, 2015).

This is an Open Access PDF ebook 978-0-9966731-1-2. It is also available through Amazon as a beautifully-printed bilingual paperback for $10.00.

There is more on Kamome here: http://humboldt.edu/kamome/

Why don’t the earthquakes line up with the San Andreas fault?

1 February 2016  |  Quake Insights

Magnitude-2.7 shock near Hollister highlights a string of quakes lighting up the San Andreas fault

A M=2.7 quake occurred on 1 Feb 2016 with a strike-slip mechanism parallel to the San Andreas, one of about 30 quakes in the past month on the same trend, about a mile west of the San Andreas. At 99, this area has the highest Seismic Hazard Rank anywhere in the US, because the active San Andreas and Calaveras faults merge here, and so ruptures on either fault could strongly shake the region from Morgan Hill, Gilroy, San Juan Bautista, Hollister, and Paicines. But why don’t the quakes line up with the San Andreas fault?

Temblor map with the pointer hovering over today’s M=2.7 quake. The seismic hazard rank here is as high as it gets anywhere in the United States.
Temblor map with the pointer hovering over today’s M=2.7 quake. The seismic hazard rank here is as high as it gets anywhere in the United States.

It turns out that the San Andreas is not vertically inclined here, probably because the fault is bending about 10° in a clockwise sense from its orientation (or ‘strike’) to the south. Careful relocation of small shocks by Janet Watt and others published in the journal Tectonics in 2014 reveal its geometry. Here is a cross-section through the San Andreas fault (SAF), Calaveras fault (CF), and Quien Sabe (QS). For the Calaveras fault, nothing is clear, but the San Andreas quakes reveal a ‘dip’ or inclination of 75°. Today’s quake lies close to this section, in which B is to the southwest and B’ is to the northwest, with the section bisecting the town of Hollister.

Seismicity cross-section with fault interpretations from Watt, J. T., D. A. Ponce, R. W. Graymer, R. C. Jachens, and R. W. Simpson (2014), Subsurface geometry of the San Andreas-Calaveras fault junction: Influence of serpentinite and the Coast Range Ophiolite, Tectonics, 33, 2025–2044, doi:10.1002/2014TC003561.
Seismicity cross-section with fault interpretations from Watt, J. T., D. A. Ponce, R. W. Graymer, R. C. Jachens, and R. W. Simpson (2014), Subsurface geometry of the San Andreas-Calaveras fault junction: Influence of serpentinite and the Coast Range Ophiolite, Tectonics, 33, 2025–2044, doi:10.1002/2014TC003561.

One can also examine a longer record of M≥2 quakes in this area and see that the pattern over the past month is typical of the past 15 years. Seismicity always lies to the west of the fault, and we should assume that the highly-active San Andreas is the culprit for these small quakes.

USGS ANSS catalog map of M≥2 earthquakes since 2000 in the vicinity of today’s quake show the same alignments as seen in the past month.
USGS ANSS catalog map of M≥2 earthquakes since 2000 in the vicinity of today’s quake show the same alignments as seen in the past month.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, California Geological Survey, and Watt et al (Tectonics, 2014)

Check your own seismic hazard for free at temblor.net

Magnitude-4.3 shock strikes on 30 Jan 2016 near Helena, Montana

31 January 2016  |  Quake Insights

On 30 January 2016, a M=4.3 shock struck at a shallow 5 km (3 mi) depth in central Montana. The shock was felt in nearby Lincoln, and in Helena, 40 miles to the southeast. There are only sporadic mapped faults in the region, the closest being the Hilger fault to the southwest, visible in the Temblor map below. This ‘normal’ fault accommodates northeast-southwest continental stretching, but since earthquake scarps over the past 10,000 or so years are not evident in the landscape, the Hilger fault probably has a low slip rate (<0.2 mm/yr). As a result, the seismic hazard rank is quite low, perhaps deceptively so.

Temblor map showing the M=4.3 event and its aftershocks, with the Hilger and Helena Valley faults to the east. There have also been some M≤3 shocks most likely associated with the Hilger fault during the past month.
Temblor map showing the M=4.3 event and its aftershocks, with the Hilger and Helena Valley faults to the east. There have also been some M≤3 shocks most likely associated with the Hilger fault during the past month.

That is because the broad Intermountain Seismic Belt, within which the quake struck, is quite active, as can be seen in the map below. The Belt stretches from Kalispell to the north to Helena, Bozeman, and into Yellowstone National Park. The largest shocks in this belt are the 1959 M=7.3 Hebgen Lake, MT, shock just outside Yellowstone in the bottom center of the map, and the 1983 M=6.9 Borah Peak, ID, shock near the bottom left corner of the map. Unlike the M=4.3 shock, both of these earthquakes ruptured long faults that had recent scarps, and so it is unclear whether a M~7 shock is possible in the vicinity of the M=4.3 event. Nevertheless, there may be undiscovered faults that link those features that have been mapped.

Map of the seismicity of Montana from 1982 to 2000, with M>2.5 shocks in yellow, and M>5.5 shocks as orange stars. Source: Montana Bureau of Mines and Geology
Map of the seismicity of Montana from 1982 to 2000, with M>2.5 shocks in yellow, and M>5.5 shocks as orange stars. Source: Montana Bureau of Mines and Geology

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Montana Regional Seismic Network, Montana Bureau of Mines and Geology

Check your seismic risk for free at temblor.net

Temblor will be presented to Gavin Newsom at a public event on Feb 11

Upcoming Event with Temblor presentation

“Innovations in Earthquake Preparedness” event will be held at UC Berkeley with Lt. Gov. Gavin Newsom at 1-3 pm on February 11; all are welcome

Lt. Gov. Gavin Newsom championed earthquake safety as Mayor of San Francisco, and as Lt. Governor, remains committed to seismic resilience for all Californians. In 2009, he launched the hugely successful mandatory retrofit program for the City: “Although there is no such thing as an earthquake-proof building, engineers agree that proper seismic retrofitting can give buildings a fighting chance against a sizeable earthquake. Now we must act decisively to protect our homes and workplaces.”

Gavin Newsom
Gavin Newsom will speak at “Innovations in Earthquake Preparedness,” a public event in Banatao Auditorium, UC Berkeley, on February 11 at 1-3 pm

The other speakers will be:

• Ross Stein, CEO and cofounder of http://temblor.net, who is also Consulting Professor of Geophysics at Stanford University, and cofounder of the Global Earthquake Model (GEM Foundation).

• Ken Goldberg, architect of http://quakecafe.org/, who is also Director of the CITRIS People and Robots Initiative, Professor in the College of Engineering, Art Practice, and School of Information, UC Berkeley, and Professor, Radiation Oncology, UC San Francisco

• Amina Assefa, Manager of UC Berkeley’s Office of Emergency Management. Amina worked extensively in the aftermath of Hurricane Katrina. New Orleans and Oakland are about the same size and character, providing invaluable experience for the next large Hayward fault quake, which looms on the horizon.

• Peggy Hellweg, Project Manager for the Earthquake Early Warning activities of the Seismological Lab of UC Berkeley, and is also a Commissioner on the California Seismic Safety Commission, which focuses on the seismic needs of the state, and promotes regulations, economic recovery, and home sale seismic disclosure.

You can check your seismic risk at Temblor.net for free

Today’s Magnitude-4.1 Joshua Tree, CA, quake and seismic swarm appear to be delayed aftershocks of the 1999 M=7.1 Hector Mine earthquake

24 Jan 2016  |  Quake Insight

The M=4.1 is part of a very shallow 12-day-long seismic swarm

A magnitude-4.1 shock struck at very shallow depth (2-5 km, or 1-3 mi) today. The event is the largest shock in a seismic swarm that begin 12 days ago; all the events in the swarm are equally shallow. The M=4.1 quake locates 4 km (2 mi) NW of a short unnamed fault oriented SW-NE, and 15 km (10 mi) east of the Lavic Lake fault rupture of the 1999 M=7.1 Hector Mine earthquake. Focal mechanisms for the event are inconsistent; it could be a ‘normal’ event parallel to the unnamed fault, or possibly a right-lateral/reverse event striking parallel to the Lavic Lake fault. Neither are what one would have expected in this fault system.

Joshua-Tree
Temblor map of today’s M=4.1 quake (red dots), the preceding 12-day-long seismic swarm (green dots) and to surrounding active faults (red lines) and the 1999 M=7.1 Hector Mine, CA, rupture.

M=4.1 was probably promoted by the M=7.1 Hector Mine quake that struck 17 years ago

What is fascinating about the Joshua Tree swarm is its relationship to the M=7.1 shock that struck 17 years ago. The swarm lies in a stress lobe that was brought closer to ‘Coulomb’ failure by the M=7.1 mainshock. The Coulomb stress assumes that faults are most likely to fail when they are sheared and unclamped.  A study by Fialko et al in Science in 2002 calculated that the site of today’s quake was strongly stressed by the 1999 mainshock. Fialko et al assumed that the surrounding faults were oriented similar to the main rupture, an assumption currently uncertain. But the M=4.1 event nevertheless points to the importance of Coulomb stress change calculations to forecast where subsequent quakes might be more likely to strike (red zones in the maps below), and less likely (blue zones).

The stress imparted by the 1999 M=7.1 Hector Mine, CA, rupture brought the site of the 24 Jan 2016 M=4.1 quake closer to failure. The permanent or ‘static’ Coulomb stress change is shown at left, and the peak dynamic stress carried by the seismic waves is shown at right. The dynamic stresses are 5-10 times larger at the site of the M=4.1 event than the static stresses, but they lasted about a minute 17 years ago, whereas the static stresses do not diminish, and so likely continue to exert an influence on seismicity. (1 MPa is about 1/4 the typical car tire pressure; 5 MPa is about the pressure in a bicycle tire). Figure modified from Yuri Fialko, David Sandwell, Duncan Agnew, Mark Simons, Peter Shearer, and Jean-Bernard Minster (Science, 2002).
The stress imparted by the 1999 M=7.1 Hector Mine, CA, rupture brought the site of the 24 Jan 2016 M=4.1 quake closer to failure. The permanent or ‘static’ Coulomb stress change is shown at left, and the peak dynamic stress carried by the seismic waves is shown at right. The dynamic stresses are 5-10 times larger at the site of the M=4.1 event than the static stresses, but they lasted about a minute 17 years ago, whereas the static stresses do not diminish, and so likely continue to exert an influence on seismicity. (1 MPa is about 1/4 the typical car tire pressure; 5 MPa is about the pressure in a bicycle tire). Figure modified from Yuri Fialko, David Sandwell, Duncan Agnew, Mark Simons, Peter Shearer, and Jean-Bernard Minster (Science, 2002).

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Caltech/USGS Southern California Seismic Network, California Geological Survey, and Fialko et al. (Science, 2002)

Follow the aftershocks and check your seismic hazard at temblor.net

Temblor: Una aplicacion para estimar nivel de amenaza sismica y costos de reforzamiento estructural

Jan 17, 2016

Tanto en la tienda de Google, como en la de Apple se pueden encontrar varias aplicaciones, que permiten convertir nuestro smarthphone en un instrumento de medicion sismica portatil. Es bastante divertido poder jugar con los sismogramas, generados artificialmente al golpear la mesa, o cualquier otra superficie cercana al lugar donde se encuentre el dispositivo. El grado de utilidad de estas herramientas rayan en la nulidad, y se acercan mas a la diversion y entretenimiento. La razon principal, quizas sea que quienes estan detras de tales aplicaciones son profesionales de la programacion meramente dicha, y aficionados a la sismologia, y no cuentan con el respaldo de expertos en el tema. Sin embargo, los institutos de investigacion de sismologia e ingenieria sismica, estan empezando a desarrollar herramientas accesibles para todos.

Hace algunos meses, un amigo, junto a un grupo de cientificos del USGS y de la Universidad de Stanford, decidieron fundar una compañia llamada Temblor, la cual incluye una aplicacion y un blog, ademas de diversos servicios en el area de la ingenieria sismica y sismologia. La aplicacion llamada “Temblor” permite, entre otras cosas, visualizar los sismos que han ocurrido en el area cercana desde donde te estan conectando, o en el area que le indiques al mapa, ademas de informacion relacionada con los posibles daños, las fallas existentes, indices de licuefaccion, entre otras cosas interesantes. La idea principal de la aplicacion es determinar el nivel de amenaza sismica del area de interes, el nivel de riesgosismico de la estructura donde vive (se necesita introducir la informacion relevante a la edificacion), y adicionalmente estima el costo necesario para hacer la edificacion sismorresistente, de acuerdo al nuevo codigo sismico de California. Es importante señalar, que todo el calculo y estimado se hace en base a los codigos y sistemas constructivos de Los Estados Unidos, el nivel de riesgo sismico, es meramente de acuerdo a la clasificacion norteamericana. Funciona con la base de datos del USGS.
El estimado de los daños se realiza de acuerdo a la posible ocurrencia de sismos de diferente magnitud, no solamente a terremotos de magnitudes grandes, como tradicionalmente se hace. Un punto a considerar es que la aplicacion no es para predecir terremotos, sino para estimar costos de refuerzo sismorresistente basado en la informacion existente.
Aunque por ahora la aplicacion este desarrollada para Los Estados Unidos de America, la idea es extenderlo a otros paises, adaptando los respectivos codigos sismicos, y las condiciones locales para cada caso. En algunas paises como Chile, algunas ciudades de Peru, Colombia y Mexico, ya hay bastante informacion disponible que podria incorporarse facilmente.
El slogan de la compañia es bastante interesante “Una solucion personal a un problema global”. En la descripcion de la misma mencionan, que la mitad de la poblacion mundial vive cerca de fallas sismicas, y por lo tanto podria sufrir los efectos de un terremoto. Sin embargo, lo peor es que mucha gente no lo sabe, y tampoco conoce el nivel de riesgo que presenta la edificacion donde habita. Desde el punto de vista economico y de inversion esto es informacion indispensable, sobre todo para las compañias aseguradoras y de real state.
Recientemente el Consejo de la ciudad de Los Ángeles, acordo ejecutar una ley que requiere que aproximadamente 15,000 edificios en la ciudad sean reforzados. La ley fue aprobada en Octubre del año 2015, poniendo fin a varias decadas de esfuerzos por fortalecer dos tipos de edificios que resultaron mortales en anteriores terremotos: Los frágiles edificios de hormigón que proliferan en los bulevares más importantes de Los Ángeles y edificios de apartamentos de estructura de madera, donde el primer piso es sumamente débil. El problema de la aplicacion de la norma radicaba principalmente en que quien asumiria los gastos, en la segunda semana de Enero de 2016, se llego al acuerdo que los gastos seran compartidos entre el dueño de la edificacion y los inquilinos, con planes de financiamiento del estado.
Asi, que partiendo de ello, anteriormente ya habia mucha informacion disponible, lo que permitio crea la compañia y aplicacion respectivamente. En los paises en vias en desarrollo queda mucho por investigar, aunque hay bastante informacion dispersa. En el caso particular de Nicaragua, y especificamente Managua, un proyecto de reahabilitacion y reforzamiento sismico quizas no sea tan complicado, considerando que las edificaciones son pequeñas y la ciudad esta en proceso de crecimiento.

http://Temblor.net

Delvin A. Martínez Hokkaido University, Japan Published in GEOSOIL

California homeowners in 100 zip codes can receive up to $3,000 for a ‘brace and bolt’ retrofit, but you need to apply by February 20

Editorial|14 January 2016

The Earthquake Brace+Bolt program is offering up to $3000 in over 100 zip codes towards a retrofit of older wood-frame homes with a ‘cripple wall’ or ‘stem wall’ (these are types of crawl spaces) below the first floor. Registration is open only from January 20 to February 20, 2016, so jump on it. Once registration ends, qualifying homeowners will be selected through a random drawing; you will be notified if chosen or are placed on a wait list.

earthquake-brace-and-bolt
Earthquake Brace and Bolt Program logo

We met with Sheri Aguirre (Managing Director of Earthquake Brace and Bolt) and Janiele Maffei (Chief Mitigation Officer of the California Earthquake Authority) in Sacramento to learn more about the program two months ago. We also talked with Margaret Vinci at Caltech, who had a very positive experience retrofitting her Pasadena home through this program; her out-of-pocket cost was only $1,000. We also met with her retrofit contractor to gain their perspective. Our only wish is that Earthquake Brace+Bolt could provide funds for many more homes. By their estimate, there are about one million California homes in need of retrofit, and so at this rate, it would take 1,000 years to get the job done. But it is nevertheless a great incentive to do something that will lower your likely cost of earthquake damage, and increase your seismic safety—at a deep discount.

Sketch to show how the crawl space is strengthened and the mudsills are bolted to the foundation in a retrofit (source: Earthquake Brace+Bolt)
Sketch to show how the crawl space is strengthened and the mudsills are bolted to the foundation in a retrofit (source: Earthquake Brace+Bolt)

Earthquake Brace + Bolt retrofit is guided by ‘Appendix Chapter A3’ for light, wood-frame houses. Qualifying foundations are concrete and reinforced masonry and include cripple walls or stem walls. In a ‘cripple wall,’ (a terrible term) there is a short wall between the foundation and first floor, so generally as you enter the home you will walk up several stairs. In the retrofit, plywood is added between the foundation and first floor to resist shear forces, and the wall is bolted to the foundation. In a ‘stem wall,’ there is a crawl space, but the first floor lies directly on the foundation. This generally involves only a bolt-down.

To decide if this makes sense for you, use the Temblor web app to determine the estimated cost and financial benefit of a retrofit for your home. Then, subtract $3,000 from the cost and see whether the net financial benefit is attractive. If your retrofit requires an engineer because the cripple walls are more than 4’ high or your home is on a steep slope, our retrofit estimate might be low. Further, retrofit costs more in the San Francisco Bay area than in greater Los Angeles because of labor rates.

Ross Stein and Volkan Sevilgen, Temblor

Data from Earthquake Brace+Bolt, and the California Earthquake Authority. We are grateful for conversations with Sheri Aguirre, Janiele Maffei, and Margaret Vinci.

Garlock fault lights up in a Magnitude-3.5 seismic swarm in the high desert of southern California

Temblor Insight | Jan 13, 2016

A M=3.5 shock at a depth of 5 km struck on the active Garlock fault.

The mainshock has a focal mechanism consistent with the left-lateral motion of this 250-km (150-mi) long and major fault that bounds the Mojave desert to the south and the Tehachapi mountains to the north. The swarm occurs where the fault bisects into two branches with a damage zone of secondary faults between them. The lack of vegetation makes the fault crystal clear in satellite imagery.

Extensive work by Sally McGill (Cal State University San Bernardino) and Kerry Sieh (Earth Observatory of Singapore) reveals a Garlock fault slip rate of 4-7 mm/yr. Given its slip rate and length, the fault should be capable of a M~7.5 earthquake every few thousand years, and smaller quakes much more frequently. Paleoseismic trenching by McGill and others bears out a 1,000-3,000 recurrence interval for larger (M7) quakes.
garlock
But the Garlock fault is also a strange beast. It is highly misaligned to accommodate the shear stress that loads the entire San Andreas system, and the misalignment increases to the east. In fact, unless the fault were extremely slippery, it would be difficult to get it to rupture at all. Think of a water melon seed: If it is wet on a table, you can push your thumb straight down on it and it will fly sideways off the table; if dry, it won’t budge. In all likelihood, the Garlock fault has rotated counterclockwise 30-40° since it formed, but is long, straight and smooth enough to keep knocking off quakes despite being a misfit by comparison to California’s great faults.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Caltech/USGS Southern California Seismic Network, California Geological Survey, and McGill et al (2008), McGill and Sieh (1992, 1993)

You can check the recent seismicity or your own seismic risk at temblor.net for free.

How to shop for a safe home in earthquake country

8 January 2016:  Editorial

We’ve all been there

You’ve finally zeroed in on a home that you can actually—somehow—afford. It’s within commute range, in a good school district, and has enough space for your family. Everything else you’ve liked has been too expensive, and everything else affordable has been too depressing. And miracle upon miracle, your bid was accepted by the seller.

Safe Home: Alley and Dan shop for homes in Sausalito, California, with their eyes open using Temblor
Alley and Dan shop for homes in Sausalito, California, with their eyes open using Temblor

Now you just want to close the deal. Soon you will be scanning title and loan doc’s and the home disclosure report as fast as you can, signing your signature a mind-numbing 140 times in front of the title officer. You don’t want to hear anything that could stand in the way of closing, and neither does your real estate agent. You just want to stop searching and start living.

But there’s a fly in this ointment

At closing ceremonies, you learn through the home disclosure natural hazards report that the house is in an active fault zone, or in a liquefaction or landslide zone, or has not been bolted to its foundation. And even this news gives you no idea what the likely cost of seismic damage could be, or how much it would cost to retrofit the home, and whether this makes sense. What are you getting yourself into?

Safe home: You really want to think twice before buying this home—on a fault and a landslide
You really want to think twice before buying this home—on a fault and a landslide.

Temblor provides a better way

We designed Temblor so that you can shop for a safe home in earthquake country with your eyes open. Just by pulling out your phone, you can learn what the seismic hazard and costs would be for any home you look at. You can compare homes in different locations to see their relative hazard and how the likely damage would change, or you can compare the damage cost of an older and newer home in the same community.

Safe home: Alley and Dan find a seismically safer home, which will lower their cost of ownership
Alley and Dan find a seismically safe home, which will lower their cost of ownership

Say, for example, you work in San Francisco (54). San Rafael (36), Burlingame (66), and Berkeley (80) are all within 50 minutes by car, but their seismic hazard rank (shown in the parenthesis) are very different. Now, let’s consider the 30-year cost of seismic damage to the same 1960 three-bedroom, two-bath, 2250 sq.ft. home in each city. Temblor makes this easy to estimate as well:  The chance of suffering $100,000 damage is 1 in 9 in San Rafael, but 1 in 6 in Berkeley. Or, let’s say you compare a Berkeley home built in 1960 with one built in 1990: The chance of $100,000 of damage over 30 years drops from 1 in 6 to 1 in 8 for the newer home.

Finally, say you buy that 1960 home. Should you retrofit it right away, and would that save you money? Temblor estimates that your retrofit would cost about $6,600 and your expected damage would drop by about $16,500, giving you a $9,900 net benefit, plus a three-fold increase in safety for your family. Now you know it’s the smart move.

Another free tool we recommend to assess your quake resilience is QuakeCAFE, which allows you to quickly assess how prepared you are compared with other Californians, and to share advice on how we could be better prepared.  It works on all screens and takes only a minute.

Ross Stein and Volkan Sevilgen, Temblor

You can check your home seismic rank at http://temblor.net

Jan 7, 2016 M=4.8 Oklahoma mainshock and its M=4.4 foreshock felt throughout north-central Oklahoma and southern Kansas

Jan 8, 2016: Quake Insights

The Jan 7, 2016 M=4.8 event followed 30 seconds after a M=4.4 at a distance of 4 km (3 mi) to the southwest. This means that the M=4.8 could have been triggered by the seismic waves of the foreshock, or it could indicate a 4-km-long rupture on a fault striking northeast.A quake of this size typically ruptures a fault area of about 3-4 km by 3-4 km, consistent with this inference. If so, the focal mechanism would indicate left-lateral slip. 

Foreshocks are rare among natural earthquakes; depending on how they are counted, they only occur several percent of the time. There were an additional 20 recorded aftershocks over an area of 7 km (4 mi). The depth of the quake could be as little as 2 km (1 mi) and as deep as 12 km (8 mi); there are inconsistencies in the current depth estimates. The other recent Oklahoma quakes were also strike-slip.

oklahomaearthquakes

Near the site of today’s temblor, there are surprisingly few deep injection wells, at least as of March 2015.  This might indicate that the well closest to these quakes was very recently drilled, or that these quakes are much farther from the fluid source than is typical.

welllocations
This map shows the ~4,500 injection wells in Oklahoma as of 19 March 2015 Source: Oklahoma Corporation Commission
oklahomadays
The past 30 days of Oklahoma seismicity correlates reasonably well with reported deep injection wells. Sources: USGS and Oklahoma Geological Survey

Ross Stein & Volkan Sevilgen, Temblor on Jan 8, 2016

Data: USGS, Oklahoma Geological Survey, Oklahoma Corporation Commission

Magnitude-4.5 Banning quake struck the San Gorgonio Pass, where the San Gorgonio thrust fault links the right-lateral San Andreas and San Jacinto faults

Jan 6, 2016:  Quake Insights

Today’s Magnitude-4.5 shock probably slipped the San Gorgonio fault Pass fault, which has a longterm slip rate of 1.4-1.5 mm/yr, making it active but not major. In contrast, the section of the San Andreas fault immediately to the east, known as the southern branch of the San Bernardino Mountain section, slips at a rapid 9.4-9.5 mm/yr and ‘dips’ or is inclined 60° to the north. The last great quake on this portion of the San Andreas struck in the late 1600’s, and given the intervening time period during which stress is being added, the fault is now capable of a M~7.8. The 1812 M~7 shock stuck on the San Andreas to the northwest of today’s shock. The San Jacinto fault to the west slips at 10.4-10.5 mm/yr, and so is also major. For these reasons, the seismic hazard rank for the site is very high, at 85.

magnitude-4-5-earthquake

The USGS reports that earthquake ruptured at 17-18 km (11 mi) depth. Many of the surrounding quakes over the past month (green dots in the map above) lie at almost this depth. In fact, this is the site of deepest earthquakes along the entire 1,000 km (600 mile) span of  the San Andreas. The focal mechanism and earthquake location are most compatible with thrust slip on the San Gorgonio fault. The quake depth and thrust motion are probably related to the 20° counter-clockwise bend of the San Andreas through the pass, which contorts the fault, uplifts the ranges, and breaks the fault into many sections.

Focal mechanism solutions furnished by the USGS and the Caltech/USGS Southern California Seismic Network. Both show largely thrust motion on an east-west striking fault
Focal mechanism solutions furnished by the USGS and the Caltech/USGS Southern California Seismic Network. Both show largely thrust motion on an east-west striking fault

The San Gorgonio fault is probably capable of a M~7 earthquake on its own, but could link up to the southern branch of the San Bernardino Mountain section of the San Andreas to produce a far larger shock. The recency of fault slip along the San Gorgonio fault is evident from the scarps (in yellow) along the base of the mountains. The mountains have been uplifted in successive earthquakes. The city of Banning lies in the down-thrown basin that has filled with sediments.

Google Earth image centered on today’s M=4.5 epicenter. The orange lines are traces of the active San Gorgonio fault. The width of the photo is about 8 km (5 mi), and San Gorgonio Pass lies 5 km (3 mi) to the east (right). Faults from the USGS and California Geological Survey.
Google Earth image centered on today’s M=4.5 epicenter. The orange lines are traces of the active San Gorgonio fault. The width of the photo is about 8 km (5 mi), and San Gorgonio Pass lies 5 km (3 mi) to the east (right). Faults from the USGS and California Geological Survey.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Caltech/USGS Southern California Seismic Network, and California Geological Survey

Learn your own hazard at http://temblor.net

Imphal, India earthquake (3 Jan 2016 M=6.7) struck in a highly active belt, and was felt in northeast India, Bangladesh, and western Myanmar

3 Jan 2016: Quake Insight

The Imphal, India earthquake struck at 55-60 km (30-36 mi) depth. Its great depth will reduce its impact on the many poorly built homes, factories, and offices in the region. Nevertheless, 224,000 people live in Imphal, where the shaking intensity predicted by the USGS PAGER system is very strong. The earthquake is the product of India’s 40 million year-long collision into Tibet, with the Indian subcontinent hurtling northward at a speed of 50 mm/yr (2”/yr), uplifting the Himalayas, deforming Southeast Asia, and extruding the crust to the northeast. The focal mechanism indicates a combination of strike-slip and thrust motion, which is characteristic of the extrusion process. The Imphal, India earthquake was preceded by a M=4 quake 22 days ago about 150 km (100 mi) to the east (see the map below); the two quakes are probably unrelated.

Epicenter of the M=6.7 Imphal India earthquake on 3 Jan 2015
Epicenter (red disk) of the Jan 3, 2016 M=6.7 Imphal India earthquake

The past century of earthquakes shows that this region has been the site of numerous damaging events, including two M=8 events, including the 1950 M=8 Assam quake 300 mi (500 km) to the north, and a M=8 quake 200 km (130 mi) to the east. Depths of 50 km are common (green dots below) in the vicinity of today’s quake.

Imphal India Earthquake (red star)
This region has been the site of numerous damaging events, the Jan 3, 2016 M=6.7 Imphal India Earthquake is shown as a red star

Focusing on M≥7.5 quakes over the past millennium, the map from Bilham (Science, 2013) below shows that the Great 1897 M=8 Shillong quake struck within 100 km (60 mi) to the west, and a series of M~7.5 shocks struck in the 1800’s along the north-oriented band of which this shock is a part.

Map of historical earthquakes, Imphal-india-earthquake shown as yellow star
Map of historical earthquakes (Bilham, Science 2013), Imphal India Earthquake is shown as a yellow star

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, ISC-GEM Seismic Catalog, and Bilham (2013)

M=4.2 Edmond earthquake on January 1, 2016, just north of Oklahoma City, continues swarm of induced seismicity

1 January 2016

Like its predecessor on 30 December 2015, the event is a strike-slip earthquake, perhaps involving left-lateral slip on a northwest-striking fault. It is somewhat shallower than it predecessor (5 km rather than 8 km), but both quakes lie below the depth of fluid injection and so might indicate fluid migration into a fault zone.
Edmunds Earthquake

Oklahoma has become the earthquake capital of the United States

Screen Shot 2016-01-01 at 11.24.48 AM
Annual Rate of earthquake sequences with at least one M≥ 3 earthquake in California (light blue) and Oklahoma (dark blue) since 1973 (Based in USGS earthquake catalog data from http://earthquake.usgs.gov). From McGarr, Bekins, Burkardt, Dewey, Earle, Ellsworth, Ge, Hickman, Holland, Majer, Rubinstein, and Sheehan (Science, 2015) http://www.sciencemag.org/content/347/6224/830

The dramatic rise in earthquake rate in Oklahoma can be traced to disposal of oil and gas field wastewater (‘produced water’) by deep injection, which intensified greatly about a decade ago (the figure below is from McGarr et al., Science, 2015). Nevertheless, the cause-effect and timing relationship between injection rates and volumes and individual earthquakes is not straightforward, and so hard to predict. The USGS is studying how to build seismic hazard assessments for states like Oklahoma, since its current hazard models—and therefore Temblor’s—do not account for this threat.

Fluid is injected into deep rock formations for many purposes

Fluid injection occurs in several US states for many reasons. Disposal of wastewater (‘produced water’) by deep (2-3 km or 1-2 mi) injection into rock formations; injection of water or CO2 into depleted oil reservoirs for enhanced oil recovery; hydraulic fracturing (‘fracking’) to enable production of oil and gas from low-permeability reservoirs; injection of CO2 into deep rock formations for permanent carbon capture and storage has been attempted as experiments to reduce the escape of greenhouse gases; and injection into geothermal reservoirs to replenish water lost to steam production or to develop enhanced geothermal systems is ongoing in places such as The Geysers in California (below).
geysers-california

Fluid injection can migrate to seismic depths, lubricating faults and triggering quakes

Most disposal wells inject into deep and highly permeable and porous sedimentary layers because these can accommodate fluids, with little or no earthquake response. Injection is purposely deep to prevent these highly toxic fluids from entering the groundwater supply. But if the injection is sufficiently deep, induced earthquakes become possible. Rarely, the fluid migrates to deeper still along faults in crystalline basement rock such as granite or basalt. These appear to be the conditions which trigger large induced earthquakes.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Oklahoma Geological Survey, and McGarr et al (Science, 2015)

 

Victoria, Canada earthquake (magnitude 4.8) widely felt in Victoria, Vancouver and Seattle

Dec 30, 2015 10:37am
The earthquake was widely felt in Victoria (home of the Pacific Geoscience Centre of the Geological Survey of Canada), Vancouver, and Seattle.
Temblor-map-for-30Dec2015-M49-quake
The 50 km (30 mi) depth places the shock on or near the megathrust surface. This is the same fault surface on which the 26 January 1700 M=9.0 Cascadia earthquake struck, rupturing for about 1,000 km (600 mi) along the Oregon, Washington, and British Columbia coastline. These giant quakes result from ‘subduction’ of the Juan de Fuca slab as it descends beneath the Pacific Northwest coastline.
Victoria-M49-map
But the focal mechanism for the M=4.9 event identifies it as a ‘normal’ fault rupture on a steeply inclined plane, which results from local tension or perhaps bending of the plate. So, both the cause of this Victoria, Canada earthquake, and any potential role in ratcheting up the stress on nearby portions of the megathrust, are currently uncertain. If the focal mechanism, location, and depth are all correct, this event occurred near—but not on—the megathrust.

Ross Stein and Volkan Sevilgen, Temblor
Data from the USGS, Pacific Northwest Seismic Network (University of Washington), Pacific Geoscience Centre (Geological Survey of Canada), and McCrory et al (2012).

You can check the aftershocks at http://temblor.net

M=4.4 San Bernardino quake strikes at the junction of three major Southern California faults

Dec 29, 2015 6:45pm

The most likely source of the earthquake is slip on the San Jacinto fault

The M=4.4 has been followed by 10 aftershocks in the first 30 min, the largest of which is magnitude 3.8. The mainshock was relatively shallow, at 4-8 km (2.5-5.0 mi) depth. The mechanism is consistent with right-lateral slip on the San Jacinto fault, which it straddles. A month ago, a preceding burst of smaller shocks struck only 5 km (3 mi) to the south, as discussed in our 17 November 2015 blog post.

greater-los-angeles-earthquake

After 159 years of quiet, the southern San Andreas is capable of a great earthquake

The quake struck where three major fault systems join: The San Andreas, San Jacinto—both right-lateral strike slip faults—and the Sierra Madre thrust fault that has uplifted the Sierra Madre Range west of the mainshock. This section of the Sierra Madre is called the Cucamonga fault. This portion of the San Andreas has not suffered a large shock since the 1857 M=7.9 Fort Tejon earthquake. In the intervening 159 years, the San Andreas has slipped about 10 feet at depths below about 15 km (10 mi), but the upper portion of the fault is frictionally locked. When stress overcomes that friction, an earthquake with about 10 feet of slip would not be unexpected, which could yield a magnitude between 7.4 and 8.0.

Earthquakes at fault junctions can sometimes be harbingers of larger quakes

Typical of fault junctions, the faults break up into many strands, and so the San Jacinto is very broad at this location. All three faults are capable of Magnitude-7 or larger earthquakes, and have relatively high slip rates. For all of these reasons, the Temblor Seismic Hazard Rank of this location is 83 out of 100.

Sometimes, but not always, large earthquakes nucleate at fault bends and junctions, as these points can probably build up greater stress than along straight and smooth fault sections. For this reason, the pattern of aftershocks and strain measured by GPS receivers will be closely monitored by the USGS and academic groups.

Ross Stein and Volkan Sevilgen, Temblor

Data from USGS, Caltech/USGS Southern California Seismic Network, and California Geological Survey.

Check your home’s seismic hazard for free at
http://temblor.net

M=4.3 earthquake in Edmond, OK (suburban Oklahoma City) this morning

29 Dec 2015, 8:30 am PST

A deep M=4.3 mainshock and shallow M=3.4 aftershock

A magnitude 4.3 shock struck this morning in Edmond, OK, shaking all of Oklahoma City and much of Tulsa. The M=4.3 quake was followed 2 hours later by a M=3.4 shock 1.5 km (1 mi) away, at a depth of 4 km (2.5 mi). During the preceding 24 hours, there were two unrelated M=3.4-3.5 quakes located 60 km (40 mi) to the north.

Slip on a left-lateral strike-slip fault is possible

The earthquake mechanism is strike-slip, with either right-lateral slip (like the San Andreas) on a northeast-striking plane, or left-lateral slip on a northwest-striking plane. A plausible alignment of recent quakes on the northwest-striking plane, as seen in the Temblor map below, makes this a more likely candidate.
Edmond Oklahoma-earthquake

Oklahoma has a higher rate of M>3 quakes than California

This earthquake was most likely triggered by enhanced oil and gas recovery in Oklahoma. The M≥3 seismicity rate has increased thirty-fold since intensive fracking and enhanced oil recovery began about a decade ago, as seen in the figure modified from Ellsworth (2013) below. As a result, Oklahoma dethroned California more than a year ago as the most seismically active state in the lower 48. Oil field operations are not causing quakes, but instead promoting them in time by reducing the friction on already-stressed natural faults.
Ellsworth-science

Interestingly, the M=4.3 quake nucleated at a depth of 8 km (5 mi), well below the depth of waste fluid injection, suggesting that some fracking fluids and other sources of “produced water” are migrating to greater depths, probably within fault zones and other fractures. But the center of the fault slip (its “centroid”) lies at about 4 km (2.5 mi), suggesting that the fault ruptured vertically toward the Earth’s surface.

Ross Stein & Volkan Sevilgen Temblor
Data from USGS, Oklahoma Geological Survey, and Ellsworth (2013)

Check your home at Temblor:http://temblor.net

Southern California: Magnitude 4.3 earthquake hit Eastern California Shear Zone

The Mojave Desert was hit by a magnitude 4.3 earthquake at 10:31 this morning (27 December 2015). Even though the epicenter was located in the sparsely populated Southern Californian high desert, the USGS PAGER system estimates that 700,000 people should have felt the earthquake. The communities of Barstow, Ridgecrest, Boron, Mojave, Lancaster, Palmdale, Edwards Air Force Base, NASA Dryden Flight Research Center and Ft. Irwin, were likely experienced shaking.
Mojave-Desert-earthquake

Today’s quake struck on a small, heretofore unknown fault that straddles active faults

Based on its USGS focal mechanism, the earthquake most likely resulted from sudden right-lateral slip (meaning that whatever side of the fault you are on, the other side moves to the right) on a minor, unnamed near-vertical fault striking (or oriented) northwest-southeast, parallel to the Harper fault zone (locally called the Gravel Hills fault) 7 miles to the southwest, and the Blackwater Fault zone 5 miles to the northeast.

ECSZ map with Reno and Barstow shocks
This event struck within what is known as the Eastern California Shear Zone (ECSZ in the map from Lee et al., Geol. Soc. Bull., 2007 above), which cuts through the Mojave Desert, continues along the east flank of the Sierra Nevada range, and extends to the eastern Tahoe basin and into westernmost Nevada, where it is called the Walker Lane (WLB above). While most of the Pacific-North America ‘transform’ or right-lateral plate motion is accommodated by the San Andreas system along coastal California, about one-quarter is splayed onto the Eastern California Shear Zone-Walker Lane, which also accommodates some Basin and Range stretching. Today’s shock struck the southern part of the Shear Zone, whereas the 23 December 2015 M=4.4 Reno shock struck near its northern end. These two moderate shocks are almost certainly unrelated, but they are evidence of the active nature of this boundary, which ruptured in the 1872 M=7.6 Owens Valley, CA, earthquake, the third largest historical California shock.

Have we underestimated the seismic hazard at the site of today’s quake?

Given that at a M=7.3 quake struck to the south of today’s M=4.3 in 1992, and a M=7.6 struck to the north in 1872, why is the Temblor hazard rank for this location only 16 out of 100? The answer is that while the Eastern California Shear Zone is laced with active faults, their slip rates are very low and uncertain, and the shear across the region measured by GPS receivers is also moderate, and so the expected quake rate and therefore frequency of shaking is much lower than along the San Andreas system. The seismic hazard rank is based on the annual probability of strong (0.4 times the acceleration of gravity) shaking, based exclusively on the USGS 2014 hazard model; it could underestimate the hazard here if the local faults slip faster than assumed.

The M=4.3 quake may have been brought closer to failure by the 1992 Landers shock

King et al (Bull. Seismol. Soc. Amer., 1994) argued that more than three-quarters of Landers aftershocks struck in regions brought closer to Coulomb failure by the M=7.3 shock. This assumes that failure was promoted on faults in which the shear stress increased, or were unclamped, by the M=7.3 quake. In their figure below, the warm colors between the white lines represent the Coulomb increases; the cool colors are where the Coulomb stress decreased, and so where the rate of shocks should have—and was largely observed to—decrease. One can see that the M=4.3 shock, along with the 1992 Barstow streak, lie in the Coulomb increase zone.

King-et-al-1994-Fig_12

Swarm-like nature of today’s shock and nearby aftershocks of the M=7.3 Landers quake

The 27 December 2015 M=4.3 mainshock was preceded over the past 1-2 days by several smaller shocks in almost the same location, which is most characteristic of seismic swarms. The event also lies about 20 miles northwest of an enigmatic streak or cluster of isolated aftershocks of the 1992 M=7.3 Landers earthquake (see the events above the word ‘Barstow’ in the map below, from Hauksson et al. (1993). Based on GPS displacement data from the 1992 quake, these aftershocks appear to accompany perhaps 20 cm (8”) of creep on an unnamed fault that was triggered by the mainshock. The 1992 streak also had a swarm-like character, with a sustained high rate of small shocks.
Hauksson-et-al
Ross Stein & Volkan Sevilgen, Temblor, Inc.

Follow aftershocks at http://temblor.net.

Data from Caltech/USGS Southern California Seismic Network, California Geological Survey, Hauksson et al (1993), King et al (1994), and Lee et al (2007).

Concord, CA: More earthquakes after the 2014 Napa quake?

Two M=1.5 quakes on December 28 in Concord appear to be part of a subtle increase in seismicity rate since the August 2014 M=6.0 Napa mainshock struck. Even without this increase, the seismic hazard rank in Concord is quite high—85. This means that compared to all other populated sites in the U.S., Concord ranks in the 85 percentile. So, only 15% of sites have a higher probability of strong earthquake shaking. This is due chiefly to its proximity to the active Concord-Green Valley fault, which slices through Concord, and lies just 2 miles east of Pleasant Hill and 5 miles east Benicia (thick red line below). Further, Pleasant Hill, and to a lesser extent, Concord, lie in liquefiable sedimentary basins, which can cause buildings to sink or tilt permanently during earthquake shaking (purple shades below).

Earthquakes as of Dec 26, 2015
Earthquakes near Concord, CA as of Dec 26, 2015

Concord-Green Valley fault is more likely to produce earthquakes after the Napa earthquake due to increased stress

Shinji Toda and I published a paper this fall in Seismological Research Letters which argues that the Napa earthquake brought parts of the Concord-Green Valley fault closer to failure. This calculation is partly supported by observed increases in the seismicity rate in the two months after the M=6.0 event compared to the 5 years beforehand (yellow-red splotches below). The rate increase in Concord was subtly visible a year ago, and seems to be sustained. The Green Valley fault slips at 6±1 mm/yr, about half of which occurs as creep. Trenching across the fault suggests a roughly 200-yr recurrence interval for M~7 shocks on the fault, and ~400 yr has elapsed time since the last large earthquake). The fault poses a substantial risk, since it bisects the city of Concord, with 200,000 residents.

Seismicity rate increase expected near Concord, CA according to toda stein
Seismicity rate increase expected near Concord CA according to Toda and Stein, 2015

Earthquakes near the city of Concord, and the Concord-Green Valley fault as a whole, should be carefully watched in the near future.

Ross Stein, Temblor CEO
Data from USGS, Berkeley Digital Seismic Network, California Geological Survey, Toda & Stein (Seismol. Res. Letts., 2015), and Lienkaemper et al (Bull. Seismol. Soc. Amer., 2014).

You can check the most recent earthquakes and calculate your own seismic risk at http://temblor.net. It’s free and ad-free.

Nevada Earthquake: A M=4.4 struck the Mount Rose Fault Zone in south Reno, Nevada

A shallow magnitude 4.4 quake struck the Mount Rose Fault Zone in south Reno, Nevada, this morning. The Nevada earthquake, its foreshocks and aftershocks struck 10 miles south of Downtown Reno, and 15 miles northeast of Mount Rose Ski Tahoe resort. The sequence has elements of swarm-like behavior, with three magnitude 3 and larger quakes in the 24 minutes preceding the M=4.4 shock.

Nevada-earthquake
Temblor Map shows that the earthquakes before and after M=4.4 Nevada earthquake in red

The Mount Rose fault zone is about 30 miles long, extending south from Reno almost to Lake Tahoe. It accommodates east-west Basin and Range stressing, and so is called a ‘normal fault.’ It has a slip rate of 1-5 millimeters each year, which makes it quite active, particularly among the normal faults that lace Nevada and eastern California. However, the Mount Rose Fault is broken up at the surface into hundreds of small segments, which makes its ability to produce a magnitude 7 earthquake uncertain. These segments might join at depth, in which case large quakes are likely. Evidence from trench excavations across some of the fault strands suggest large slip events have occurred in the past several thousand years, with slip of 2-4 meters, as would occur in magnitude 7 earthquakes. Thus, the potential for larger quakes is quite real and important.

Ross Stein, Temblor CEO
Data from the USGS,  Nevada Seismological Laboratory, Nevada Bureau of Mines and Geology.

The perfect gift: An earthquake emergency kit

There’s been a lot of political talk recently about protecting our safety. But for those of us living in earthquake country, perhaps the most important way to make our family safer is to give an earthquake emergency kit. My wife and I, together with my brother and his partner, gave all of our grown children and their significant others Quake Emergency Kits for Chanukah. It’s a way to turn the anxiety we all share into an expression of our love. And I promise you, much of the gear will be used and appreciated long before the next quake hits.

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Here’s what’s in the earthquake kit I gave my kids

At Temblor, we have been giving a lot of thought into what should go into the kit, having spent time in earthquake aftershock zones in Turkey, Japan, Idaho, and California. I keep one kit in the trunk of my car, one in my wife’s car, and another in our home. How many kits to have and where to keep them depends on your lifestyle, but for those who commute in your own car, the trunk is king.

One of the most important kit components is an old warm jacket, gloves, woolen hat, and walking shoes. Just toss them into a backpack along with the other gear. After a major quake, we will most likely be communicating by cell, and also using our cell phones for news, so the phones will need to be constantly recharged. A solar charger of 7W or more, with a battery of 10,000 mAh, would take care of two cell phones each day with decent sunlight. A headlamp is vastly better than a flashlight, because you are hands-free, it points where you are going, and there could be broken glass around you. Go with at least 80 lumens, and have at least 3 Lithium batteries for it, which last much longer than normal batteries, and have a 20-year shelf life.

Then, you need non-perishable food and water to last several days in sealed 4-year pouches, a good first aid kit with lots of bandages, toiletries, any meds you cannot do without, a cold pack for burns, work gloves, a good face mask for concrete dust, a knife and whistle. I keep the flat, international orange whistle on my key chain; it’s always there if I need to call for help, and I never lose my keys. I keep a headlamp on my bedside table. I end up using the clothes, first aid kit, headlamp, and charger all the time.

We have worked with Suzanne Tateosian, proprietor of Burlingame-based Earth Shakes, who has been making great kits for 20 years. Use promo code ‘temblor’ to get a 5% discount on her offerings. Let it be the fulfillment of a New Years resolution: To prepare rather than deny.

Ross Stein
Temblor, Inc. CEO


Click here to buy earthquake emergency kits. Use promo code ‘temblor’ for a 5% discount.

Retrofit: What’s wrong with this home appraisal?

Last week, our home was appraised for a mortgage refinance. I asked the certified real estate appraiser if he wanted to know if we had retrofit. He said, “No, it has no impact on the value.” He checked only that the water heater was strapped to the wall.

Retrofit: How much is your home worth?
How much is your home worth? A seismic retrofit should add value to the home appraisal.

A few weeks ago, in separate conversations, I asked several leading Bay Area real estate agents whether a retrofit increases the home sales price. Each said ‘no.’ A marble countertop in a half-bathroom would increase the home’s value about five times its cost, but something that would drastically reduce the damage in a quake has zero impact on its price. Could we be this shallow? This is nuts. Until a home appraisal includes the retrofit, we are doomed to delude ourselves about the true cost of home ownership, and the key benefit of retrofit, in earthquake country.

But it gets worse.

Earlier this year, we were asked by a young couple with a baby on the way to about their quake risk. They bought a beautiful 50-year-old apartment in a ‘tenants-in-common’ building in San Francisco. Any insurance or retrofit decision would have to be approved jointly by the six owners, and so they wanted facts to make any case. In addition to securing their china, vases, electronics and glassware, we advised them to get a retrofit quote. They engaged an engineering firm, which submitted an estimate. But the couple couldn’t make heads or tails of it, so the husband showed the quote and the building plans to his father, who happens to be a contractor. Guess what: The building had already been retrofit when it was remodeled as ‘tenants-in-common.’ When the couple bought the apartment, the retrofit wasn’t even part of the sales pitch.

But it gets even worse.

The engineering company that submitted the quote was the same company that had designed the retrofit beforehand.

So, the system is broken.

Not only does retrofit not to add sale value in this market, but perhaps it is even hidden for fear that the mere mention of earthquakes will frighten buyers.

Temblor’s goal is to change this dynamic, to shine a light on retrofit and increase its value. Like any other improvement, a homeowner should know that the money invested in retrofit will be rewarded not only if a quake strikes, but also when they sell.

Ross S. Stein, Temblor cofounder & CEO

Todays’ Gerlach, Nevada, M=4.1 quake highlights a geothermal swarm

The Gerlach, Nevada M=4.1 is the second largest quake in the past month, part of a swam of 231 events near the Nevada-Oregon border. The swarm lies at the junction of the Warner Valley fault and the Guano Valley fault zone, neither of which is very active.

Nevada Magnitude 4.1 earthquake 6 Dec 2015
Gerlach Nevada Magnitude 4.1 earthquake 6 Dec 2015

Swarms are most common in geothermal areas, such as the Geysers in northern California, the Salton Sea in southern California, and the Coso area in eastern California. The hot water tends to make faults more slippery, permitting them to creep, accompanied by sustained bursts of earthquakes.

The Nevada swarm is taking place within the Surprise Valley (SV) geothermal belt, with groundwater temperatures in excess of 100°C (yellow dots) and 160°C (red dots). Map is from Faulds et al. (2011).
The Nevada swarm is taking place within the Surprise Valley (SV) geothermal belt, with groundwater temperatures in excess of 100°C (yellow dots) and 160°C (red dots). Map is from Faulds et al. (2011).

 

The underlying cause of many of these geothermal areas are the stretching and thinning of the Earth’s crust in the Basin and Range province (whose northwest boundary is the brown curve in the Faulds et al., 2011 map), which brings the hotter lower crust closer to the Earth’s surface, where it heats, mobilizes, and mixes deep crustal fluids and shallow groundwater.

Deep M=4.3 quake stuck today southwest of the recent M=4.7 shock 6 days ago

A M=4.3 quake struck the town of Waynoka, OK. The quake resulted from sudden slip on a strike-slip fault, similar to the two M=4.7 quakes that struck over the past 17 days, but this one was deeper, at 10-12 km (6-7 mi). All of the larger quakes stuck along a 100 km (60 mi) northeast trend. This quake and its predecessors were likely triggered by deep fluid injection, but at 12 km, this quake stuck far below the injection depth, which might indicate that the fluids are infiltrating to considerable depths.

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M=4.3 Oklahoma earthquake

Oklahoma: A second Magnitude 4.7 earthquake strikes in 11 days

A second M=4.7 earthquake shock struck northern Oklahoma at 3:49 am local time, at a shallow depth of 5 km (3 mi). The shock was felt as far away as Oklahoma City and Tulsa in Oklahoma, and Wichita and Dodge City in Kansas. The first M=4.7 struck on November 19 about 40 km (25 mi) to the west. It is unlikely that the two quakes are related, except that both are associated with deep wastewater injection associated with oil exploration and production activities.

Oklahoma-Temblor

Earthquake rate in Oklahoma exceeds that of California

In the past decade, the rate of earthquakes in Oklahoma has increased by a factor of 30 over the previous 35 years, as reported by William Ellsworth of the USGS in Science (2013). Today, the M≥3 quake rate in Oklahoma exceeds that of California. A new study by Susan Hough and Morgan Page, both at the USGS, and published in Bulletin of the Seismological Society of America, finds that most of the Oklahoma quakes since the 1930’s were themselves associated with wastewater injection, and so the factor of 30 underestimates the increase over the natural quake rate. In addition to the 2011 M=5.7 Prague, Oklahoma earthquake, the largest quake in the area was the 1952 M=5.7 El Reno, Oklahoma earthquake.

There is an active fault in Oklahoma, and so the background rate of quakes—those not associated with oil field operations—cannot be zero. The Meers fault can be seen on Temblor maps. It produced large earthquakes about 1,000 and 2,000-3,000 years ago. Today’s M=4.7 quake was a ‘strike-slip’ event, the same kind of motion as occurs on the Meers fault. Further, injection of wastewater primarily lubricates natural faults, and so these faults must already be stressed by tectonic forces to be able to trigger an earthquake. In this sense, oil field operations are greatly accelerating a natural process rather than replacing it by a man-made one.

Peru-Brazil border struck by two M=7.6 earthquakes

Earthquakes occurred 5 minutes and about 30 miles (50 km) apart.

The two events also had approximately the same type of faulting (focal mechanism). Such “doublets” rarely occur. The earthquakes are extremely deep (600 km or 360 miles); very few quakes strike deeper than these, because the rocks melt and do not behave in a brittle manner. At this site, the Nazca plate subducts beneath the South America plate at a rate of about 70 mm/yr (3 inches per year). Peru-brazil-earthquakes
The events were probably widely felt but shaking was very light because of the extreme depth.

Earthquakes occurred in the area of former deep earthquakes

One can see from the map below that a large number of similarly deep (purple) quakes have struck during this century in about the same location. The focal mechanism suggests tensional stress, perhaps because the descending plate is bending at this depth.
Peru-brazil-earthquakes

Ongoing Earthquake Swarm near Nevada-Oregon Border Suggests Creep on the Guano Valley Fault

Some 237 earthquakes occurred in the last 30 days

Temblor Map shows the epicenters of the earthquakes. You can take a look at the interactive Temblor map. It is updated every five minutes. Show me the quakes

Earthquake swarm near Nevada Pregon border

1915 Pleasant Valley earthquake with magnitude 7, occurred 150 miles to the southeast of the earthquake swarm

The largest quake so far is M=4.2. This is probably a seismic swarm associated with fault creep. Both nearby faults are caused by Basin and Range stretching, and are inclined (‘dip’) to the west, with very low slip rates (<0.2 mm/yr). The strain rate and seismic hazard are low, but are higher 20 miles to the west along the Surprise Valley fault. The closest large quake this century struck 150 miles to the southeast, in the 1915 M=7 Pleasant Valley event.

This post is prepared by Ross Stein at Temblor, Inc. You can check earthquakes and faults around you or learn your own seismic risk for free.

Oklahoma rattled by a magnitude 4.6 quake

A mid-size earthquake with magnitude 4.6 occurred in Oklahoma on Nov 20, 2015 16:40:40. This is one of 232 earthquakes recorded in Oklahoma in 30 days.  The epicenter  is 120 mile North of Oklahoma city and it is probable to far to be felt there.

See the earthquakes that hit Oklahoma in the last 30 days

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Click here for interactive map

Oklahoma earthquake with magnitude 4.7 is the largest of 200 earthquakes in the last 30 days

Oklahoma earthquake hit rural part of the state

Oklahoma earthquake was felt strongly in Cherokee, Helena, and Alva, lighter shaking was felt in Kiowa, Fairview, Enid and Edmond. There are reports that residents in Wichita and Oklahoma City also felt the Temblor.
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Show me the Oklahoma earthquake in Temblor App


Warning: Fracking related earthquakes are not incorporated in standard seismic hazard assessments, so hazard values are underestimated. Soon, Temblor will incorporate increased hazard by induced seismicity.

California earthquake with magnitude 3.5 struck where three loaded faults meet

Today’s California earthquake lies in one of the most active knots of seismicity. The temblor struck at the junction of the major San Jacinto fault, which extends to the southeast, and the Cucamonga fault, extending to the west as part of the Sierra Madre fault zone. The California earthquake and its aftershocks also lie just 6 miles from the San Andreas fault, just to the north. All three faults are capable of Magnitude 7 or larger earthquakes, and all are highly active. For all of these reasons, the Temblor Seismic Hazard Rank of this location is 81 out of 100.

Let me check my seismic rank


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Could the magnitude 6.5 Greece earthquake trigger another large shock?

Not only have there been many large shocks in this region during the past century (eight M≥6.5 events within 80 km, a rate of one a decade), but they often strike in pairs. M=6.5 and M=6.8 events stuck one day apart in 1953, and M=6.4 and M=6.5 events struck two months apart in 1948 on either side of the epicenter of the 2015 shock. Thus, the possibility that the 17 November shock could be part of a twin cannot be discounted.

17 Nov M=6.5 Nidri Greece earthquake trigger

The 17 November 2015 Mw=6.5 Nidri Greece earthquake struck in a highly active region in northwest Greece, at the junction of three active faults. Broadly, the ‘Nubia’ tectonic plate is impinging on Greece from the east at a rate of 6 millimeters per year, shoving the crust of the Ionian Sea beneath mainland Greece.

Large earthquakes often start or strike at the intersection of faults, as appears occurred here. The plate boundary is fractured into several active faults, including the Kephallonia fault to the south of the epicenter, which slips in a right-lateral sense at a rate of 5-20 mm/yr. (‘Right-lateral’ means that whatever side of the fault you are on, the other side slides to the right). For comparison, the San Andreas (California), and North Anatolia (Turkey) faults slip at about 25 mm/yr. Extending north of the epicenter is the right-lateral Lefkada fault, slipping at 4-8 mm/yr in a right-lateral sense. Intersecting the epicenter from the northwest is the Kerkya thrust fault, slipping 1-2 mm/yr. The mechanism of this quake suggests that the fault ruptured the Kephallonia-Lefkada system, with some thrust motion as well.

[Data from USGS, SHARE, and the ISC-GEM seismic catalog; map base from Google Earth. Interpretation by Ross S. Stein, Temblor, Inc. Nov 17, 2015]

You can follow any earthquake at http://temblor.net

A large magnitude 6.5 Greece earthquake felt most of Greece

A large earthquake occurred at 2015-11-17 07:10:08 (UTC) near west coastline of the country. The Greece earthquake felt strongly in the cities: Lefkada, Nidri, Preveza, Aneza, Vonitsa, Agios Spyridon. It also felt in Patra, Larisa, Vlore, Bitola, and Thessaloniki.

Video show tall buildings have shaken strongly during the Greece earthquake. Watch the video

USGS estimates that some 7 Million people felt the quake, and over 70,000 of them felt a very strong shaking.

USGS map shows that the Greece earthquake was felt most of southern Greece.

Greece earthquake felt area

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Temblor Map

Earthquakes have historically caused widespread damage across this region

Earthquakes have historically caused widespread damage across central and southern Greece, Cyprus, Sicily, Crete, the Nile Delta, Northern Libya, the Atlas Mountains of North Africa and the Iberian Peninsula. The 1903 Magnitude 8.2 Kythera earthquake and the 1926 Magnitude 7.8 Rhodes earthquakes are the largest instrumentally recorded Mediterranean earthquakes. Source:USGS

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Underwater pier detonated on old San Francisco Bay Bridge on Nov 14 shows up in Temblor map equivalent to Magnitude 2 quake.


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Underwater pier detonated on old Bay Bridge early Saturday shows up in Temblor map equivalent to Magnitude 2 quake.

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