From temblor: “New findings clarify the seismic risk in the Pacific Northwest”


From temblor

July 24, 2018
David Jacobson, M.Sc.

New findings have shown how the cities of Seattle and Portland could fare in a Cascadia Subduction Zone earthquake. (Photo from Fine Art America)

How bad would a Cascadia Subduction Zone earthquake be for the Pacific Northwest?

In the last month, several studies were published which not only showcase the dangers posed by this 1,000 km-long (600 mi) plate boundary, but highlight where ruptures may be most likely. The findings show that in the cities of Portland and Seattle, the quake could leave hundreds of thousands of properties damaged and destroyed, and that in places like Seattle, which lies in a sediment-filled basin, shaking could be much more severe.

Three years ago, Kathryn Schultz’ Pulitzer Prize-winning New Yorker essay, The Really Big One, thrust the Cascadia Subduction Zone into the public spotlight. While the convergent plate boundary, which extends from Vancouver Island at its north end to California’s Cape Mendocino at the south, had been known to scientists for decades, the article renewed public interest and scientific focus.

Major population centers exposed to significant risk

In the event of a Cascadia Subduction Zone earthquake, over 200,000 homes are likely to be damaged in the city of Portland, according to a study by the Oregon Department of Geology and Mineral Industries (DOGAMI).

The two largest cities in the Pacific Northwest, Seattle and Portland, are home to several million people. In the event of a M=9 earthquake, which is what Cascadia is capable of, the impact would be severe. Part of this is due to proximity to the plate boundary to theses urban centers, but also the geology.

The city of Seattle, the nation’s fastest-growing city, lies in the Puget lowland on the shores of Puget Sound and Lake Washington. While the location creates an ideal trade gateway, it also means the city lies atop a deep basin. This has startling consequences for shaking, according to a recent study by scientists at the University of Washington, the USGS, and University of Southern California. They looked at how buildings ranging from 4-40 stories high would sway (engineers call this “drift”) in simulated earthquakes, comparing the ride in the Seattle basin, and outside it. They found that within the basin, buildings swayed at least three times more than outside of it because of stronger, slower shaking. Thus could result in much greater levels of damage throughout the city, and longer recovery times.

In Portland, 233 km (145 mi) south of Seattle, the situation is not much better. The Oregon Department of Geology and Mineral Industries (DOGAMI) recently published an updated scenario of what a M=9 Cascadia event could do to the city. By assessing the shaking throughout the metropolitan area, they found approximately 38-39% (235,000) of the city’s buildings would suffer some level of damage. This emphasizes, is that in the event of a Cascadia event, the impacts will not only be extremely severe, but extremely widespread.

Where is a great rupture most likely to happen?

While scientists do not know where a rupture will strike, there are clues that point to areas which may be more susceptible. Two of these are ‘locking,’ and seismic ‘tremor.’ As tectonic plates move against one another, stress builds up. Eventually, the stress reaches a critical level, the fault leaps forward and an earthquake takes place. Where plates are “locked,” the amount of stress that can be built up is greatest. Therefore, identifying the most locked portions of the Cascadia Subduction Zone sheds light on areas of greatest risk. The figure below shows that along the plate boundary, locking is greatest in Washington on the one hand, and Southern Oregon and Northern California on the other. Northern Oregon shows quite a bit.

The area between the bold dashed east-west lines is not strongly locked and produces few tremors, so it is less likely to rupture in a megaquake than the fault segments to the north and south of the dashed lines. The figure is from Bodmer et al., 2018, based on geodetic data from Schmalzle et al., 2014 as well as tremor density from the Pacific Northwest Seismic Network.

Seismic tremor, which accompanies slow slip events, is common along parts of the Cascadia subduction zones. Tremor seems to be another indication that the fault is locked above a certain depth, but is firing off in very small shocks and slippage just below that depth.

In fact, over the last two weeks, tremor has picked up in Northern Washington, Southern Oregon, and Northern California, as the map from the Pacific Northwest Seismic Network below shows.

Cascadia subduction zone

Cascadia plate zones

Slow slip events are not like regular earthquakes, which last for tens of seconds, but instead last for days to weeks. These events locate just below the locked portions of the fault, and are accompanied high frequency vibration or ‘tremor.’

While scientists are still unsure if periods of intense tremor, such as has occurred for the past two weeks, can presage large earthquakes, strongly-locked tectonic plates tend to produce the largest and most frequent megaquakes. And, a recent study by University of Oregon and University of New Mexico scientists shows that the higher levels of locking and tremor in certain parts of the Pacific Northwest are likely permanent features.

What does this mean for the Pacific Northwest?

Seattle, Portland, and Vancouver B.C. all lie within the zones of elevated tremor and strong locking. In contrast, Eugene lies inland of the portion of the megathrust that is not strongly locked and that produces less tremor. Therefore, the new evidence only confirms and highlights the risk for Vancouver, Seattle, and Portland, and perhaps reduces it for Eugene.

References [sorry, no links]

John M. Bauer, William J. Burns, and Ian P. Madin, Earthquake Regional Impact Analysis for Clackamas, Multnomah, and Washington Counties, Oregon, Oregon Department of Geology and Mineral Industries Open-File Report O-18-02

N. Marafi, M. Eberhard, J. Berman, E. Wirth, A. Frankel, and J. Vidale. Effects of Simulated Magnitude 9 Earthquake Motions on Structures in the Pacific Northwest. Proceedings of the 11th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Los Angeles, CA. 2018.

Bodmer, M., Toomey, D. R., Hooft, E. E. E., & Schmandt, B. (2018). Buoyant asthenosphere beneath Cascadia influences megathrust segmentation. Geophysical Research Letters, 45. https://

John E. Vidale and Heidi Houston, Slow slip: A new kind of earthquake, January 2012, Physics Today

See the full article here .


Please help promote STEM in your local schools.

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