From temblor: “Ancient rock structures guided rupture pathway in Australian quake”

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From temblor

July 16, 2020
Helen Santoro, freelance science journalist, (@helenwsantoro)

Early one May morning in 2016, a magnitude-6.0 earthquake ripped through central Australia, causing a 13-mile (21-kilometer) stretch of land to shift upwards by up to three feet (approximately one meter). Typically, an earthquake of this magnitude results in far larger ground displacements and jagged ruptures — but this rupture was long and smooth, puzzling scientists at the University of Melbourne.

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The magnitude-6.0 quake produced a remarkably linear surface rupture. Credit: Dan Clark, Commonwealth of Australia (Geoscience Australia).

Generally, ruptures that break the surface are rough and curved, says Januka Attanayake, a seismologist at the university and lead author on the study. “This one was different.”

A history of larger ground displacements

Although Australia is located in the middle of the Indo-Australian tectonic plate, far from a plate boundary where large quakes typically occur, the continent still has a history of destructive earthquakes. A magnitude-5.6 earthquake in 1989, for example, hit the harbor city of Newcastle and caused 13 deaths and $4 billion in damage — making it one of Australia’s worst natural disasters. Luckily, most earthquakes of this magnitude happen in remote areas far away from cities and towns.

The majority of these moderate earthquakes also occur on faults that don’t generate clear surface ruptures. If an earthquake generates a surface offset, or “fault scarp,” researchers get a chance to make direct observations of the fault surface and can better understand the processes behind the rupture. Any fault scarp needs to be documented immediately following an earthquake, before the forces of nature — wind, water, animal, etc. — work to erase any clues that could give scientists valuable insight into the rupture process.

Uncovering the foundation of the smooth rupture

As luck may have it, the 2016 earthquake created a clear surface rupture — providing a perfect opportunity for scientists from the University of Melbourne to study the tremor. The earthquake originated near the Petermann Ranges, a mountain range that extends almost 200 miles (320 kilometers) across central Australia that was formed around 550 million years ago.

After the earthquake, the team trekked out into the field to create a detailed map of the fault scarp. They used satellite-based global positioning system (GPS) data to map the feature from above and found a relatively smooth and straight 13-mile (21-kilometer) scarp. To see the fault underground, the group used data from seismometers — instruments that record ground motion — to detect and locate aftershocks. These smaller quakes result from the redistribution of stress following a larger shock and tend to cluster along the fault surface that ruptured in the main quake. They therefore can be used to map the extent of the fault below the surface.

Attanyake and his team discovered that the pattern of aftershocks followed along a known subsurface rock structure, suggesting that the surface that ruptured during the quake was related to this feature. In fact, the orientation of the structure seemed to control the path of the rupture.

Old rocks dictate modern earthquakes

Around 550 million years ago India slammed into Western Australia, causing the Petermann mountains to form. The grinding together of these land masses at extreme pressure and temperature deep within the Earth’s crust caused weak zones of rock to form. Over time, as Earth’s surface was slowly eroded away, these zones made their way closer to the surface.

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Weak zones within old rocks in the Petermann Ranges are a path of least resistance for stress to concentrate in the crust. Here the orientation of these weak rock units is shown with the dotted line and arrow. Credit: Fabian Prideaux

Stress that builds in the crust through time causes rocks to break through the path of least resistance — in the case of the 2016 earthquake, one of these weak zones.

“We don’t know why this particular weak layer ruptured, but that layer is what caused the long, straight line,” Attanayake explained. “The weak mechanics of the rocks allowed it to easily react to the earthquake,” meaning that earthquake essentially took advantage of the presence of this weak layer.

Earthquakes like this that occur far from plate boundaries are rare, says John Paul Platt, a professor of geology at the University of Southern California. But he adds, they “can be particularly dangerous because they affect areas where buildings are not constructed to withstand earthquakes.” Understanding where these types of ruptures may occur could be vital for disaster preparation. This latest study suggests that in some cases, the rocks at the surface and at depth could give scientists clues about where a future quake could occur.

Further Reading

Attanayake, J., T. R. King, M. C. Quigley, G. Gibson, D. Clark, A. Jones, S. L. Brennand, and M. Sandiford (2020). Rupture Characteristics and Bedrock Structural Control of the 2016 Mw 6.0 Intraplate Earthquake in the Petermann Ranges, Australia, Bull. Seismol. Soc. Am. 110, 1037–1045, doi: 10.1785/ 0120190266

Salleh, Anna (2009). Mystery mountain range explained. Retrieved July 1, 2020, from https://www.abc.net.au/science/articles/2009/12/10/2765285.htm

Verdouw, E. (2018, September 02). On this day: Newcastle earthquake strikes. Retrieved June 19, 2020, from https://www.australiangeographic.com.au/blogs/on-this-day/2013/11/on-this-day-newcastle-earthquake-strikes/

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