From temblor: “Magnitude 7.1 earthquake rips northwest from the M6.4 just 34 hours later”

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From temblor

July 6, 2019
Tiegan Hobbs

The M 6.4 earthquake loaded the site where the M 7.1 shock nucleated. Now, the M 7.1 has extended the original rupture to the northwest, as well as to the southeast, where it kisses the major Garlock Fault.

Citation: Ross S. Stein, Tiegan Hobbs, Chris Rollins, Geoffrey Ely, Volkan Sevilgen, and Shinji Toda, (2019), Magnitude 7.1 earthquake rips northwest from the M6.4 just 34 hours later, Temblor, http://doi.org/10.32858/temblor.037

Rupture of a Previously Unknown Fault

The town of Ridgecrest was not done shaking after a magnitude 6.4 earthquake on the morning of July 4. An M=7.1 shock ruptured for at least 35 km (20 mi) from the 4 July 2019 epicenter, towards the northwest, and perhaps also for 25 km to the southeast. It is astonishing that there is no continuous mapped fault at the ground surface, despite the near absence of vegetation that can otherwise hide faults. Numerous other faults have been mapped in this region, trending predominantly in a north-south direction, somewhat different than this earthquake. The aftershock alignment, however, is very straight in a northwest-southeast trend, suggesting that beneath the surface must lie a continuous fault. We strongly suspect that the rupture is right-lateral (whichever side you are on, the other moves to the right). The trend is parallel to the San Andreas Fault, but has a strike (or compass orientation) more westerly than most of the nearby surrounding faults.

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Map of the past 40 hours of earthquakes from the USGS (ANSS) catalog, with the inferred sense of fault slip represented by the gray half-arrow pairs. This gives the impression of a northwestward rupture of perhaps 30 km length, which is very short for such a large shock. Because the USGS website is experiencing problems, this might be an incomplete portrayal.

Did the Rupture Unzip to the Northwest Only, or Also to the Southeast?

Without knowing about this fault, there was no reason to suspect that such a large earthquake could occur to the north of the July 4 rupture. Fortunately, this is a remote location, with even fewer people living to the northwest of the mainshock than the south.

While much of the seismicity in the last 48 hours has fallen along two nearly linear faults, aftershocks of this magnitude 7.1 earthquake have formed a cluster to the northwest of the main rupture fault. This cluster, near Little Lake, CA, is approximately 15 km (9 miles) south of the Coso Geothermal Area. That geothermal region is home to abundant seismicity [Hauksson & Unruh, 2007] which is often clustered in swarms at its periphery. All events in this swarm, as of midnight local time on July 5th, are shallower than 10 km depth, consistent with previous swarms in this area.

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This Temblor app map with another 2 hours of events gives a different impression of the M 7.1 aftershocks than the initial USGS map, suggesting that the rupture does not simply extend to the northwest. Based on these aftershocks it appears ‘bilateral’, meaning that the fault unzipped both to the northwest and southwest, for a total length of up to 55 km. This would be more consistent with its magnitude, as a strike-slip M 7.1 typically has a length of about 50 km. If this is correct, then parts of the Garlock Fault might also be brought closer to failure.

Chain Reaction

In retrospect, the M 6.4 quake on July 4 can now be regarded as a foreshock of the M 7.1. While generally uncommon, there are many recent examples of occurrences similar to this. The 14 April 2016 M 6.0 Kumamoto shock was followed 28 hours later by a M 7.0 quake on 15 April 2016 that ruptured two major faults that were brought closer to failure by the first event. The 3 November 2002 M 7.9 Denali earthquake on the Denali Fault was preceded by a M 6.7 shock on the Fault on 23 October 2002, 11 days beforehand.

The epicenter of the M 7.1 was Loaded by the M 6.4 Earthquake

Preliminary Coulomb stress transfer calculations reveal that the epicenter of the M 7.1 shock was brought 2 bars closer to failure by the M 6.4 shock. In other words, the 4 July event stoked the fire for the 5 July magnitude 7.1 earthquake. This large stress jump very likely played a role in the triggering of the second event. In fact, it would not be incorrect to say that the M 7.1 was an unusually large aftershock of the M 6.4, rather than the M 6.4 being a foreshock of the M 7.1.

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Coulomb stress changes on nearby faults, as a result of the 4 July 2019 M=6.4 earthquake near Ridgecrest. The approximate location of the 5 July M=7.1 earthquake is indicated by the purple star, near the northwesterly extension of the fault that ruptured on the 4th of July. Stress in the region of the M=7.1 event was increased by roughly 2 bars following the M=6.4 earthquake.

Aftershocks Propagating Towards the Garlock Fault

Seismicity between the M=7.1 at 8:19pm and midnight (local) has continued to the northwest and southeast. At the time of writing, 12:10am (local) the closest aftershock is within a few kilometers of the nearby Garlock Fault, which runs east-west between the Eastern California Shear Zone and the San Andreas Fault. Changes in stress on this major fault can have major implications for the nearby city of Los Angeles, and so will be closely monitored in the coming days. At this time, the USGS has forecasted that in the next week there is only a 9% chance of an aftershock which is equal to or larger than this M=7.1 event.

References

Hauksson, E., & Unruh, J. (2007). Regional tectonics of the Coso geothermal area along the intracontinental plate boundary in central eastern California: Three‐dimensional Vp and Vp/Vs models, spatial‐temporal seismicity patterns, and seismogenic deformation. Journal of Geophysical Research: Solid Earth, 112(B6).

See the full article here .


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Earthquake Alert

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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.

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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
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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.

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

Learn more about EEW Research

ShakeAlert Fact Sheet

ShakeAlert Implementation Plan