From temblor: “Offshore El Salvador earthquake strikes location of deadly M=7.7 event”



April 4, 2018
David Jacobson
Ross Stein, Ph.D.

El Salvador’s capital city of San Salvador experienced light shaking in Monday’s M=5.9 offshore earthquake. (Photo from: Lonely Planet)

A location with deadly history

On Monday, a M=5.9 earthquake struck off the coast of El Salvador. Fortunately, the quake did not cause damage, though it was felt in the capitals of both Guatemala and El Salvador, which combined, are home to nearly 4 million people. The location of this earthquake makes it of importance as it is nearly identical to a M=7.7 earthquake in 2001 that claimed nearly 1,000 lives, generated thousands of landslides, and caused millions in damage.

This Temblor map shows the location of Monday’s M=5.9 earthquake off the coast of El Salvador. Fortunately this earthquake did not cause damage, though it is in almost the exact location of a deadly M=7.7 quake in 2001.

An earthquake with a unique origin

Given the location of this earthquake, one would expect it to be a small subduction zone event. However, based on the focal mechanism produced by the USGS, this was not a megathrust event. The USGS focal mechanism shows that this earthquake was either pure right-lateral or compressional on a nearly vertical fault. At this stage, we cannot be sure which is correct. Regardless though, it is curious given the regional tectonics, as just off the coast of El Salvador is the Middle America Trench, where the Cocos Plate subducts beneath the Caribbean Plate at a rate of 70-75 mm/yr. Therefore, Monday’s earthquake can be considered to have an exotic focal mechanism.

Just as Monday’s event had an exotic focal mechanism, so did the M=7.7 in 2001. That earthquake was extensional in nature and also occurred within the overriding Caribbean Plate. Having two moderate to large magnitude earthquakes in the same location, with extremely variable focal mechanisms could indicate some type of internal breakup of the Caribbean Plate or faulting of the descending slab. Regardless, it shows how this area is susceptible to earthquakes with varying motion.

In the M=7.7 earthquake in 2001, thousands of landslides were triggered in El Salvador.

A larger earthquake is possible

Even though this region is no stranger to large earthquakes, prior to the M=7.7 in 2001 there had been 26 M=6+ earthquakes within 250 km in the preceding 40 years, there has not been a recent large megathrust event. In fact, going back to 1700 using the Global Earthquake Model’s Global Historical Archive and Catalog, we still see no large megathrust earthquake. While could mean that the region does not experience large subduction zone events, there is the possibility of larger events.

This map shows M=6+ earthquakes off the coast of El Salvador since 1900. As one can see, Monday’s event struck right next to the deadly M=7.7 event in 2001. This map also highlights how the region is very seismically active and how residents of Central America should be aware of their seismic hazard.

We know this by using the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor. This model uses global strain rates and the last 40 years of earthquake to forecast the likely earthquake magnitude in your lifetime anywhere on earth. In the figure below, one can see that in the location of Monday’s earthquake, up to a M=7.5 is likely. While this means that Monday’s M=5.9 earthquake should not be considered surprising, it also shows how seismically at risk Central America is and that locals should be aware of the threat beneath their feet.

This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for much of Central America. This model uses global strain rates and the last 40 years of earthquake to forecast the likely earthquake magnitude in your lifetime anywhere on earth. In this figure one can see that in the location of Monday’s M=5.9 earthquake, a M=7.25+ is likely.

References [sorry, no ;inks, but 1 doi]
Martin Vallee and Michel Bouchon, The 13 January 2001 El Salvador earthquake: A multidata analysis, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B4, 2203, doi:10.1029/2002JB001922, 2003
Global Earthquake Model (GEM) Global Historical Archive and Catalog

See the full article here .

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Stem Education Coalition

Earthquake Alert


Earthquake Alert

Earthquake Network project Earthquake Network is a research project which aims at developing and maintaining a crowdsourced smartphone-based earthquake warning system at a global level. Smartphones made available by the population are used to detect the earthquake waves using the on-board accelerometers. When an earthquake is detected, an earthquake warning is issued in order to alert the population not yet reached by the damaging waves of the earthquake.

The project started on January 1, 2013 with the release of the homonymous Android application Earthquake Network. The author of the research project and developer of the smartphone application is Francesco Finazzi of the University of Bergamo, Italy.

Get the app in the Google Play store.

Smartphone network spatial distribution (green and red dots) on December 4, 2015

Meet The Quake-Catcher Network

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).

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

ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States


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 in 2018.

Watch a video describing how ShakeAlert works in English or Spanish.

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. ShakeAlert can give enough time to slow 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 in 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” 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 joined by Oregon and Washington in April 2017. This West Coast-wide “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.


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

Learn more about EEW Research

ShakeAlert Fact Sheet

ShakeAlert Implementation Plan