From temblor : “Surprising recharacterization of earthquake risk along a strand of the San Andreas”


From temblor

April 20, 2021
Ben Wolman (@bythewolman)

The San Andreas Fault (US) is as close to a celebrity as geological features can get — it even has a movie named in its honor.

Since its formal identification in the late 19th century, the fault has been analyzed, dated, mapped and modeled by thousands of scientists. But its southernmost section, which is divided into strands like the frayed ends of a rope, still puzzles scientists.

The northern and central sections of the San Andreas have ruptured relatively recently, geologically speaking (in 1906 and 1857, respectively), producing magnitude-7+ earthquakes (Fialko, 2006). The southernmost section, southeast of Los Angeles, however, last ruptured in 1726 and has accumulated significant strain since. This is partly why people often say it’s “overdue” for a big quake (though faults can’t really be overdue).

A recent study published in Science Advances suggests that the Mission Creek strand of the San Andreas, which runs along the northeastern side of the Coachella Valley, is the dominant fault at this latitude, accounting for about 90% of the overall slip rate of the southern San Andreas Fault system. That means the Mission Creek strand — not the strands previously identified as accumulating the most strain — could host the next major earthquake on the southern San Andreas.

The southern San Andreas Fault consists of multiple strands. The Mission Creek strand may be a bigger risk for Southern California than previously thought. Credit: modified from Kimberly Blisniuk.

Slipping and straining

Slip rates describe the speed at which the two sides of a fault move relative to each other. Slip rates are typically ascertained through geologic measurements of landforms offset by fault movement, such as jags in alluvial fans, beheaded stream channels (those cut off from their headwaters), and vegetation lineaments (where dense vegetation meets less-dense vegetation in an abrupt line, likely due to a fault cutting off groundwater where the line occurs). Geodetic data obtained by ground motion observed in GPS or radar imaging can also be used to model slip rates.

Previous geologic and geodetic data suggested that one piece of the San Andreas in the Coachella Valley called the Banning strand was likely responsible for the bulk of the slipping northwest through the San Gorgonio Pass. The Banning and Mission Creek strands run roughly parallel to one another. The new study investigates the slip rates from two new locations in the valley.

Offset landforms

Kimberly Blisniuk, an earthquake geologist and geochronologist at San Jose State University (US), and her team started by reconstructing and dating landform offsets in the Indio Hills (Banning) and Pushawalla Canyon (Mission Creek). They used lidar imaging and field mapping to determine the offset of ancient stream channels and other landforms. Then the team combined two different dating techniques — uranium-thorium dating of soil and beryllium-10 dating of surface exposures — to provide a minimum age estimate and a maximum age estimate for the landforms.

The team noted that in Pushawalla Canyon, channels come out of a steep mountain front and hit the valley and aggrade in a unique stairstep-like terrace pattern, says Richard Heermance, a geologist at California State University-Northridge (US), who was not involved in the new research. By matching the deposits with their likely places of origin, and with “a distance and an age for each surface when they were just forming,” the team computed slip rates by simply dividing distance by age, Heermance says. The uniqueness of the Pushawalla Canyon landforms enabled this mapping, he adds. “That part of the story is great.”

Beheaded channels cut by a strand of the San Andreas fault. Credit: Kimberly Blisniuk.

The landform changes and dating together indicate that the Mission Creek strand at this latitude, previously thought to be inactive, has hosted the most earthquakes in this region over the last 100,000 years, Blisniuk and her team reported.

Slip on a different fault strand

In addition, Blisniuk and her team found that the Mission Creek strand at Pushawalla Canyon appears to slip approximately 0.9 inches (21.6 millimeters) per year — compared to the Banning strand’s 0.1 inches (2.5 millimeters) per year. That means in the last 295 years, the Mission Creek strand has accumulated 20-30 feet (6-9 meters) of elastic strain, a measure of stress. Think of elastic strain like a rubber band pulled taut: If you stop pulling on the rubber band, strain is released and it can go back to its normal shape. But if it’s pulled too tight for too long, it will snap and release that strain in the form of energy. Rocks along a fault do the same, releasing the strain in an earthquake. Thus, the Mission Creek strand may instead hold the lion’s share of earthquake potential at Pushawalla Canyon.

Risks to Los Angeles

The findings could be important for the densely populated Los Angeles area. “Before, we only had this one path where a southern San Andreas Fault earthquake could rupture through the greater Los Angeles area,” Blisniuk says. “Now we’re seeing that actually, kind of like the [2019] Ridgecrest earthquakes, which occurred on faults that weren’t identified, there are faults that we’ve identified as likely inactive, that may still be active.”

Future southern strand risk mapping

“This study has highlighted the need for more detailed studies,” Heermance says, especially through San Gorgonio Pass northwest of the Banning and Mission Creek strands where much of the strain in this region is currently thought to be accumulating. But Heermance says the approximately 0.9 inches (21.6 millimeters) of annual slip found in the study cannot yet be definitively attributed to the entire Mission Creek strand northwest of Pushawalla Canyon: It’s still an open question, he says, noting that future fault mapping should help reduce the uncertainty.

Blisniuk doing field work along the southern San Andreas Fault. Credit: Thomas Rockwell, San Jose State University (US).

Blisniuk agrees further landform offset analyses and dating of additional sites along the strands are needed. She says she’s excited by the promise of new data to be unearthed at these strands. “This is one of the best-studied faults in the world. And now with new technology and new dating techniques, we can test all of these [earthquake] models.” And those new data are suggesting that there’s so much to learn, and there’s so much to still investigate. “The past is the key to the present.”


Blisniuk, K., Scharer, K., Sharp, W.D., Burgmann, R., Amos, C., Rymer, M., 2021. A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California. Sci Adv 7, eaaz5691.

Fialko, Y., 2006. Interseismic strain accumulation and the earthquake potential on the southern San Andreas fault system. Nature 441, 968–971.

Further Reading

Guns, K.A., Bennett, R.A., Spinler, J.C., McGill, S.F., 2020. New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California. Geosphere 17, 39–68.

See the full article here .


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Earthquake Alert


Earthquake Alert

Earthquake Network projectEarthquake 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



About Early Warning Labs, LLC

Early Warning Labs, LLC (EWL) is an Earthquake Early Warning technology developer and integrator located in Santa Monica, CA. EWL is partnered with industry leading GIS provider ESRI, Inc. and is collaborating with the US Government and university partners.

EWL is investing millions of dollars over the next 36 months to complete the final integration and delivery of Earthquake Early Warning to individual consumers, government entities, and commercial users.

EWL’s mission is to improve, expand, and lower the costs of the existing earthquake early warning systems.

EWL is developing a robust cloud server environment to handle low-cost mass distribution of these warnings. In addition, Early Warning Labs is researching and developing automated response standards and systems that allow public and private users to take pre-defined automated actions to protect lives and assets.

EWL has an existing beta R&D test system installed at one of the largest studios in Southern California. The goal of this system is to stress test EWL’s hardware, software, and alert signals while improving latency and reliability.

Earthquake Early Warning Introduction

The United States Geological Survey (USGS), in collaboration with state agencies, university partners, and private industry, is developing an earthquake early warning system (EEW) for the West Coast of the United States called ShakeAlert. The USGS Earthquake Hazards Program aims to mitigate earthquake losses in the United States. Citizens, first responders, and engineers rely on the USGS for accurate and timely information about where earthquakes occur, the ground shaking intensity in different locations, and the likelihood is of future significant ground shaking.

The ShakeAlert Earthquake Early Warning System recently entered its first phase of operations. The USGS working in partnership with the California Governor’s Office of Emergency Services (Cal OES) is now allowing for the testing of public alerting via apps, Wireless Emergency Alerts, and by other means throughout California.

ShakeAlert partners in Oregon and Washington are working with the USGS to test public alerting in those states sometime in 2020.

ShakeAlert has demonstrated the feasibility of earthquake early warning, from event detection to producing USGS issued ShakeAlerts ® and will continue to undergo testing and will improve over time. In particular, robust and reliable alert delivery pathways for automated actions are currently being developed and implemented by private industry partners for use in California, Oregon, and Washington.

Earthquake Early Warning Background

The objective of an earthquake early warning system is to rapidly detect the initiation of an earthquake, estimate the level of ground shaking intensity to be expected, and issue a warning before significant ground shaking starts. A network of seismic sensors detects the first energy to radiate from an earthquake, the P-wave energy, and the location and the magnitude of the earthquake is rapidly determined. Then, the anticipated ground shaking across the region to be affected is estimated. The system can provide warning before the S-wave arrives, which brings the strong shaking that usually causes most of the damage. Warnings will be distributed to local and state public emergency response officials, critical infrastructure, private businesses, and the public. EEW systems have been successfully implemented in Japan, Taiwan, Mexico, and other nations with varying degrees of sophistication and coverage.

Earthquake early warning can provide enough time to:

Instruct students and employees to take a protective action such as Drop, Cover, and Hold On
Initiate mass notification procedures
Open fire-house doors and notify local first responders
Slow and stop trains and taxiing planes
Install measures to prevent/limit additional cars from going on bridges, entering tunnels, and being on freeway overpasses before the shaking starts
Move people away from dangerous machines or chemicals in work environments
Shut down gas lines, water treatment plants, or nuclear reactors
Automatically shut down and isolate industrial systems

However, earthquake warning notifications must be transmitted without requiring human review and response action must be automated, as the total warning times are short depending on geographic distance and varying soil densities from the epicenter.