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

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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

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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

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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.

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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).

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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

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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

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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.

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