From temblor : “Submarine mountains can subdue earthquakes”

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From temblor

August 23, 2021

Scientists surveying the seabed off New Zealand’s east coast have uncovered undersea mountains that help explain mysterious slow-motion earthquakes.

By Erin Martin-Jones, Ph.D., Department of Earth Sciences, University of Cambridge (UK)

Earth’s tectonic plates are constantly jostling for space — colliding and diving under one another in a dance that sculpts dramatic mountain chains, fuels volcanic eruptions and delivers earth-shattering tremors. But sometimes these forces can have more subtle impacts. Take, for instance, silent earthquakes or “slow-slip events,” which can move at slow-motion speeds, stretching their ruptures over weeks to months. Often, no one feels a thing, and these events go undetected even by seismometers.

So why do some faults slip suddenly and set off deadly earthquakes while others slide slowly and stealthily? A new study [Nature] suggests that off the coast of New Zealand, where thousands of small quakes occur each year, excess water locked within undersea mountains, or “seamounts,” can promote the silent sliding linked to slow-motion earthquakes.

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Map of Hikurangi Subduction Zone, showing locations where electromagnetic receivers were deployed to collect data. Credit: Christine Chesley, using GeoMapApp and data from William Ryan et al., Geochemistry, Geophysics, Geosystems (2009).

The Hikurangi Margin Subduction Zone

To understand slow-slip earthquakes off New Zealand’s eastern coast, a team of researchers led by Christine Chesley of Columbia University’s Lamont-Doherty Earth Observatory first had to figure out a way to peer into the depths of a subduction zone.

The team used electromagnetic methods to essentially take an MRI scan of the seabed along the Hikurangi Margin where the Pacific Plate dives beneath the Australian Plate. That subduction motion along the margin is partly responsible for the more than 15,000 earthquakes in the region each year. Most are so small that they go unnoticed, but between 150 and 200 are large enough to be felt.

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The research vessel hauls in one of the receivers used to take electromagnetic measurements of the seabed. Credit: Kerry Key.

This subduction zone poses a significant earthquake and tsunami hazard to coastal communities in New Zealand, but the largest earthquakes only seem to occur toward the south of the margin — and scientists want to know why. “One of the fascinating things about this area, and why so many have studied it, is the puzzling variation in earthquake hazards over a very small area,” Chesley says.

Although large earthquakes haven’t struck the North Island in roughly the last 200 years, evidence of ancient quakes is written in the rocks along the coastline, which have been jolted upward by past seismic events.

Diving beneath the hidden depths of silent earthquakes

In December 2018, the research team began a month-long deep-sea cruise, collecting profiles of the seafloor in the northern part of the subduction zone margin, which is studded with large seamounts. “Although other studies have suggested that seamounts may contribute to small, rather than large and destructive earthquakes, it’s been unclear exactly how those mountains interact with the seafloor as they are subducted,” says Chesley.

Chesley’s eye was drawn to two seamounts: the Tūranganui Knoll, located about 110 kilometers southeast of the east coast city of Gisborne, and an unnamed one that is closer to the margin and is currently being subducted. A cluster of tiny earthquakes related to a 2014 slow-slip event occurred around the second seamount, which first began subducting about a million years ago.

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Christine Chesley and Eric Attias operate the Scripps Undersea Electromagnetic Source Instrument (SUESI) during a deep-tow. SUESI is attached to the ship via a coaxial cable and must be “flown” about 100 meters above the seafloor. Credit: Kerry Key.

Peeling back the layers of a seamount

Chesley’s team’s electric conductivity survey revealed that each seamount was made up of layers of varying porosity, which held water and conducted electricity differently. Each had a solid core surrounded by a layer of loose, cindery material that acts a bit like a sponge. In fact, the team found that seamounts lock away three to five times more water than typical oceanic crust. This water can act as a lubricant to help tectonic plates glide into Earth’s interior without setting off a large earthquake.

“It makes a lot of sense, knowing how they form, but we really weren’t expecting them to be such heterogeneous masses of rock,” says Chesley. She noted that the nuance in material can really affect how the subducting plate moves and expels water when it is subducted.

Because both seamounts had a similar structure, the researchers think that even actively subducting seamounts retain their structural strength — so much so that they can damage the overriding plate, causing tiny faults that dissipate the energy and result in slow-slip events.

New methods

This study is the first to use electromagnetic methods to map out water trapped in rocks beneath the seafloor offshore, says Susan Ellis, a geophysicist at GNS Science, who was not involved in the study. “Mapping the structure of the seafloor is extremely challenging and has only recently become viable. This research is at the cutting edge of new geophysical imaging methods,” Ellis says.

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Electromagnetic receivers can be seen on the back deck of the R/V Roger Revelle during particularly rough seas. Credit: Kerry Key.

“These results are very exciting … they show just how subducting topography can impact water content,” she adds. That, in turn, reveals the type of slipping. “Understanding why slow-slip events occur is critical for estimating New Zealand’s earthquake and tsunami hazard.”

Factoring underwater oddities into hazard models

“Seamounts are very common on the seafloor, but hazard models currently don’t consider how they contribute to slow-slip events,” says Chesley. “Now we know that we need to take seafloor topography into account — otherwise we’re not getting the full picture.”

But Chesley and her team note that slow-slip earthquakes aren’t always subdued. In 1947, two unusual tsunamis were both associated with slow-slip behavior. And because they weren’t preceded by shaking, there was little warning.

“Future work in other locations of the margin, and in other subduction zones with and without seamounts, will help us understand whether there are any other factors that also contribute to slow-slip events,” says Ellis. Or that contribute to a larger event, for that matter.

References:

Chesley, C., Naif, S., Key, K., & Bassett, D. (2021). Fluid-rich subducting topography generates anomalous forearc porosity. Nature, 595(7866), 255-260. doi.org/10.1038/s41586-021-03619-8

Sun, T., Saffer, D. and Ellis, S., 2020. Mechanical and hydrological effects of seamount subduction on megathrust stress and slip. Nature Geoscience, 13(3), pp.249-255. doi.org/10.1038/s41561-020-0566-5

Wallace, L.M., Webb, S.C., Ito, Y., Mochizuki, K., Hino, R., Henrys, S., Schwartz, S.Y. and Sheehan, A.F., 2016. Slow slip near the trench at the Hikurangi subduction zone, New Zealand. Science, 352(6286), pp.701-704. doi.org/10.1126/science.aaf2349

Wang, K., & Bilek, S. L. (2011). Do subducting seamounts generate or stop large earthquakes? Geology, 39(9), 819-822. doi.org/10.1130/G31856.1

See the full article here .


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Please help promote STEM in your local schools.

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Earthquake Alert

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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.

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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

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

QuakeAlertUSA

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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.