From temblor: “M=7.1 earthquake collapses buildings in Mexico City on the 32nd anniversary of a deadly M=8.0 quake”

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temblor

September 19, 2017
David Jacobson, Temblor
Professor Shinji Toda,
IRIDeS, Tohoku University, Japan

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This Temblor map shows the location of today’s M=7.1 earthquake just south of the country’s capital, Mexico City.

At 1:14 p.m. local time, a M=7.1 earthquake struck just south of Puebla, Mexico, and 120 km from Mexico City, where almost 9 million people reside. From the initial USGS ShakeMap, severe shaking was felt close to the epicenter, while in Mexico City, they would have experienced moderate to strong shaking, enough to cause significant damage. Ironically, this earthquake comes on the 32nd anniversary of a deadly M=8.0 earthquake in Mexico City which killed over 5,000 people and caused billions in damage. Furthermore, as an observance to the anniversary, several buildings held earthquake drills earlier in the day. Unlike today’s quake, which struck southeast of the city, that earthquake was centered over 350 km to the southwest of the capital.

Based on reports and photos, we know that at least 42 people are confirmed to have died, and buildings have collapsed in Mexico City. The USGS PAGER system estimates that economic losses could reach $1 billion, with up to 1,000 fatalities. This deadly quake comes less than 2 weeks after a M=8.1 earthquake shook the Chiapas region to the southeast. While the magnitude of that quake was significantly larger than today’s, shaking in Mexico City was greater today, given the proximity of the epicenter to the city.

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Today’s M=7.1 earthquake south of Mexico City resulted in significant damage throughout the city. (Photo from: Ronaldo Schemidt/Agence France-Presse — Getty Images)

Despite the fact that just offshore of Mexico is the Middle America Trench, where the Cocos plate subducts beneath the North American plate at a rate of approximately 76 mm/yr, today’s event, like the earthquake on Sept 7, was extensional in nature. Depending on the subduction model used, today’s earthquake could have either been within the subducting Cocos plate (Franco et al., 2005), or the overriding North American plate (Hayes et al., 2012). This difference is a matter of how much the dip of the subducting slab shallows. Professor Shinji Toda at IRIDeS, Tohoku University, Japan, says that while intraslab earthquakes are typically not as destructive as subduction zone events, their sources are totally invisible and are thus extremely unpredictable. Additionally, he suggests that while inland Mexico is dominated by subduction megathrust events and onshore active faults, a flattened slab layer could be a third source of large earthquakes.

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This figure, which has been modified from Franco et al., 2005 shows the location of the two large recent earthquake in Mexico. Additionally, it shows the rupture areas of other large historic earthquakes in the country. Lastly, this figure highlights how both of the large earthquakes in the last two weeks were likely intraplate events within the subducting Cocos Plate.

From the focal mechanism and location of today’s event, it may have struck within the Trans-Mexican Volcanic Belt. While this chain of active volcanoes is the product of subduction at the Middle America Trench, there is regional extension. Throughout this volcanic belt, which runs across central Mexico, there are pronounced east-west-oriented extensional faults. Based on historical earthquakes, there is no known subduction zone seismicity below the Trans-Mexican Volcanic Belt (Suter et al., 2001). This means that any earthquake within this zone is likely to be extensional.

From the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, today’s M=7.1 earthquake just south of Mexico City can be considered surprising. This model uses global strain rates and the last 40 years of seismicity to forecast the likely earthquake magnitude in your lifetime anywhere on earth. From this model, which is shown below, one can see that in the location of today’s event, the likely magnitude is M=6.5-6.75. Having said that, in 1999, a M=7.0 earthquake struck just roughly 100 km to the east. That too was an extensional earthquake likely associated with the Trans-Mexican Volcanic Belt. As more information comes in on this earthquake, we will either update this blog, or post an entirely new one.

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This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for much of Mexico as well as the locations of today’s M=7.1 earthquake, and the M=8.1 quake less than two weeks ago. What this map shows is that based on their magnitudes, both of these quakes should be considered relatively surprising.

References [No links]
USGS
European-Mediterranean Seismological Centre
Max Suter, Margarita Lopez Martınez, Odranoel Quintero Legorreta, and Miguel Carrillo Martınez, Quaternary intra-arc extension in the central Trans-Mexican volcanic belt, GSA Bulletin; June 2001; v. 113; no. 6; p. 693–703
Franco et al., Propagation of the 2001-2002 silent earthquake and interplate coupling in the Oaxaca subduction zone, Mexico, Earth Planets and Space · October 2005

See the full article here .

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Stem Education Coalition

You can help many citizen scientists in detecting earthquakes and getting the data to emergency services people in affected area.
QCN bloc

Quake-Catcher Network

The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers. With your help, the Quake-Catcher Network can provide better understanding of earthquakes, give early warning to schools, emergency response systems, and others. The Quake-Catcher Network also provides educational software designed to help teach about earthquakes and earthquake hazards.

After almost eight years at Stanford, and a year at CalTech, the QCN project is moving to the University of Southern California Dept. of Earth Sciences. QCN will be sponsored by the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Center (SCEC).

The Quake-Catcher Network is a distributed computing network that links volunteer hosted computers into a real-time motion sensing network. QCN is one of many scientific computing projects that runs on the world-renowned distributed computing platform Berkeley Open Infrastructure for Network Computing (BOINC).

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The volunteer computers monitor vibrational sensors called MEMS accelerometers, and digitally transmit “triggers” to QCN’s servers whenever strong new motions are observed. QCN’s servers sift through these signals, and determine which ones represent earthquakes, and which ones represent cultural noise (like doors slamming, or trucks driving by).

There are two categories of sensors used by QCN: 1) internal mobile device sensors, and 2) external USB sensors.

Mobile Devices: MEMS sensors are often included in laptops, games, cell phones, and other electronic devices for hardware protection, navigation, and game control. When these devices are still and connected to QCN, QCN software monitors the internal accelerometer for strong new shaking. Unfortunately, these devices are rarely secured to the floor, so they may bounce around when a large earthquake occurs. While this is less than ideal for characterizing the regional ground shaking, many such sensors can still provide useful information about earthquake locations and magnitudes.

USB Sensors: MEMS sensors can be mounted to the floor and connected to a desktop computer via a USB cable. These sensors have several advantages over mobile device sensors. 1) By mounting them to the floor, they measure more reliable shaking than mobile devices. 2) These sensors typically have lower noise and better resolution of 3D motion. 3) Desktops are often left on and do not move. 4) The USB sensor is physically removed from the game, phone, or laptop, so human interaction with the device doesn’t reduce the sensors’ performance. 5) USB sensors can be aligned to North, so we know what direction the horizontal “X” and “Y” axes correspond to.

If you are a science teacher at a K-12 school, please apply for a free USB sensor and accompanying QCN software. QCN has been able to purchase sensors to donate to schools in need. If you are interested in donating to the program or requesting a sensor, click here.

BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience.BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.

Earthquake safety is a responsibility shared by billions worldwide. The Quake-Catcher Network (QCN) provides software so that individuals can join together to improve earthquake monitoring, earthquake awareness, and the science of earthquakes. The Quake-Catcher Network (QCN) links existing networked laptops and desktops in hopes to form the worlds largest strong-motion seismic network.

Below, the QCN Quake Catcher Network map
QCN Quake Catcher Network map

Earthquake country is beautiful and enticing

Almost everything we love about areas like the San Francisco bay area, the California Southland, Salt Lake City against the Wasatch range, Seattle on Puget Sound, and Portland, is brought to us by the faults. The faults have sculpted the ridges and valleys, and down-dropped the bays, and lifted the mountains which draw us to these western U.S. cities. So, we enjoy the fruits of the faults every day. That means we must learn to live with their occasional spoils: large but infrequent earthquakes. Becoming quake resilient is a small price to pay for living in such a great part of the world, and it is achievable at modest cost.

A personal solution to a global problem

Half of the world’s population lives near active faults, but most of us are unaware of this. You can learn if you are at risk and protect your home, land, and family.

Temblor enables everyone in the continental United States, and many parts of the world, to learn their seismic, landslide, tsunami, and flood hazard. We help you determine the best way to reduce the risk to your home with proactive solutions.

Earthquake maps, soil liquefaction, landslide zones, cost of earthquake damage

In our iPhone and Android and web app, Temblor estimates the likelihood of seismic shaking and home damage. We show how the damage and its costs can be decreased by buying or renting a seismically safe home or retrofitting an older home.

Please share Temblor with your friends and family to help them, and everyone, live well in earthquake country.

Temblor is free and ad-free, and is a 2017 recipient of a highly competitive Small Business Innovation Research (‘SBIR’) grant from the U.S. National Science Foundation.

ShakeAlert: Earthquake Early Warning

The U. S. Geological Survey (USGS) along with a coalition of State and university partners is developing and testing an earthquake early warning (EEW) system called ShakeAlert for the west coast of the United States. Long term funding must be secured before the system can begin sending general public notifications, however, some limited pilot projects are active and more are being developed. The USGS has set the goal of beginning limited public notifications by 2018.

The primary project partners include:

United States Geological Survey
California Governor’s Office of Emergency Services (CalOES)
California Geological Survey
California Institute of Technology
University of California Berkeley
University of Washington
University of Oregon
Gordon and Betty Moore Foundation

The Earthquake Threat

Earthquakes pose a national challenge because more than 143 million Americans live in areas of significant seismic risk across 39 states. Most of our Nation’s earthquake risk is concentrated on the West Coast of the United States. The Federal Emergency Management Agency (FEMA) has estimated the average annualized loss from earthquakes, nationwide, to be $5.3 billion, with 77 percent of that figure ($4.1 billion) coming from California, Washington, and Oregon, and 66 percent ($3.5 billion) from California alone. In the next 30 years, California has a 99.7 percent chance of a magnitude 6.7 or larger earthquake and the Pacific Northwest has a 10 percent chance of a magnitude 8 to 9 megathrust earthquake on the Cascadia subduction zone.

Part of the Solution

Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of the ShakeAlert system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm’s way. This can be done by detecting the first energy to radiate from an earthquake, the P-wave energy, which rarely causes damage. Using P-wave information, we first estimate the location and the magnitude of the earthquake. Then, the anticipated ground shaking across the region to be affected is estimated and a warning is provided to local populations. The method can provide warning before the S-wave arrives, bringing the strong shaking that usually causes most of the damage.

Studies of earthquake early warning methods in California have shown that the warning time would range from a few seconds to a few tens of seconds, depending on the distance to the epicenter of the earthquake. For very large events like those expected on the San Andreas fault zone or the Cascadia subduction zone the warning time could be much longer because the affected area is much larger. ShakeAlert can give enough time to slow and stop trains and taxiing planes, to prevent cars from entering bridges and tunnels, to move away from dangerous machines or chemicals in work environments and to take cover under a desk, or to automatically shut down and isolate industrial systems. Taking such actions before shaking starts can reduce damage and casualties during an earthquake. It can also prevent cascading failures in the aftermath of an event. For example, isolating utilities before shaking starts can reduce the number of fire initiations.

System Goal

The USGS will issue public warnings of potentially damaging earthquakes and provide warning parameter data to government agencies and private users on a region-by-region basis, as soon as the ShakeAlert system, its products, and its parametric data meet minimum quality and reliability standards in those geographic regions. The USGS has set the goal of beginning limited public notifications by 2018. Product availability will expand geographically via ANSS regional seismic networks, such that ShakeAlert products and warnings become available for all regions with dense seismic instrumentation.

Current Status

The West Coast ShakeAlert system is being developed by expanding and upgrading the infrastructure of regional seismic networks that are part of the Advanced National Seismic System (ANSS); the California Integrated Seismic Network (CISN) is made up of the Southern California Seismic Network, SCSN) and the Northern California Seismic System, NCSS and the Pacific Northwest Seismic Network (PNSN). This enables the USGS and ANSS to leverage their substantial investment in sensor networks, data telemetry systems, data processing centers, and software for earthquake monitoring activities residing in these network centers. The ShakeAlert system has been sending live alerts to “beta” test users in California since January of 2012 and in the Pacific Northwest since February of 2015.

In February of 2016 the USGS, along with its partners, rolled-out the next-generation ShakeAlert early warning test system in California. This “production prototype” has been designed for redundant, reliable operations. The system includes geographically distributed servers, and allows for automatic fail-over if connection is lost.

This next-generation system will not yet support public warnings but does allow selected early adopters to develop and deploy pilot implementations that take protective actions triggered by the ShakeAlert notifications in areas with sufficient sensor coverage.

Authorities
The USGS will develop and operate the ShakeAlert system, and issue public notifications under collaborative authorities with FEMA, as part of the National Earthquake Hazard Reduction Program, as enacted by the Earthquake Hazards Reduction Act of 1977, 42 U.S.C. §§ 7704 SEC. 2.

For More Information

Robert de Groot, ShakeAlert National Coordinator for Communication, Education, and Outreach
rdegroot@usgs.gov
626-583-7225

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