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

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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).

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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/

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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)

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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

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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

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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

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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

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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.

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