New Algorithm GFAST Enhances the ShakeAlert Earthquake Early Warning System

The Pacific Northwest is earthquake country. Oregonians and Washingtonians may experience multiple types of earthquakes in their lifetimes, from moderate-sized earthquakes like the 2001 Nisqually event to a devastating megathrust earthquake on the Cascadia Subduction Zone. But the ShakeAlert® Earthquake Early Warning System can alert people before dangerous shaking arrives, potentially saving lives.

The ShakeAlert System, managed by the United States Geological Survey (USGS), is constantly being upgraded to improve alert speed and accuracy. It is extremely important to be able to quickly estimate the location and magnitude of major earthquakes so that alerts can rapidly be delivered to everyone in the affected areas. Scientists at the Pacific Northwest Seismic Network (PNSN) have developed a new geodetic algorithm called GFAST (Geodetic First Approximation of Size and Time) that will improve ShakeAlert’s ability to quickly characterize the magnitude of the next Big One. ShakeAlert is the world’s first earthquake early warning system that incorporates geodetic data and algorithms. 

ShakeAlert uses real-time data from over 1500 seismic sensors and now, with the incorporation of the GFAST algorithm, utilizes data from over 760 Global Navigation Satellite System (GNSS) sensors for rapid earthquake detection. GNSS includes the well-known US-based Global Positioning System (GPS) as well as other satellite-based positioning systems used across the globe. Seismometers measure how quickly the earth is shaking in terms of velocity or acceleration. GNSS geodetic sensors measure how far the ground moves up, down, or sideways as a result of an earthquake. Small earthquakes cause small localized shifts. Larger magnitude earthquakes have greater velocity and acceleration of shaking as well as cause more extensive permanent ground displacement. During a Cascadia Subduction Zone earthquake, the ground could shift down and westward by several meters! 

The Pacific Northwest Seismic Network operates most of the seismic stations in the Pacific Northwest. The geodetic stations used for GFAST are maintained by a range of other partners, including the EarthScope Consortium and Central Washington University.

a Regional seismic stations alone cannot accurately estimate the magnitudes (M) of the largest earthquakes. They saturate around M7, meaning they have difficulty discerning a M7 earthquake from a M9 earthquake using initial measurements. That could lead the ShakeAlert System to initially underestimate the magnitude of a Cascadia Subduction Zone earthquake, which would cause the ShakeAlert System to alert fewer people than needed. Because geodetic stations measure ground displacement, they can provide more accurate magnitude estimates for very large earthquakes. In a Cascadia Subduction Zone earthquake, this means a broader area and more people would be alerted, enabling them to take immediate life-saving protective actions.

GFAST was developed by PNSN researchers Brendan Crowell and Carl Ulberg, who work at the University of Washington. Research was also contributed by Diego Melgar, who directs the Cascadia Region Earthquake Science Center at the University of Oregon, and Jessica Murray of the USGS. Crowell and Melgar began developing the theory that peak ground displacement is analogous to earthquake magnitude in the early 2010s as part of their PhD research at the Scripps Institution of Oceanography. Crowell then used funds donated to the PNSN by the Gordon and Betty Moore Foundation and theAmazon Catalyst Program to develop the methodology and code base for the early GFAST algorithm and convert it to a format that was compatible with the ShakeAlert System. Additional funds from the USGS Earthquake Hazards and NASA Disasters programs helped to further refine the GFAST architecture.

In the early 2020s, Ulberg and others in ShakeAlert’s Software Management Working Group began integrating GFAST messages into the ShakeAlert solution aggregator. This aggregator was designed to evaluate the results of the two other earthquake detection algorithms already used by ShakeAlert and provide a definitive estimate of the detected earthquake’s size and location. Those existing algorithms, EPIC (Earthquake Point‐source Integrated Code) and FinDer (Finite‐Fault Rupture Detector), solely use data from seismic stations.

Ulberg created new logic within the ShakeAlert solution aggregator and GFAST itself in order to decide when and how to use GFAST in addition to EPIC and FinDer. For example, GFAST had to understand how many geodetic stations needed to provide data and how much displacement was required before an estimated magnitude would be considered reliable. It also had to weed out background “noise” from geodetic stations that could lead to false alerts. GFAST cannot reliably detect small and moderate earthquakes and works best in conjunction with seismic algorithms which can determine when and where earthquakes originate. For this reason, GFAST will start augmenting EPIC and FinDer for M7+ earthquakes and will become increasingly important the larger an earthquake grows. 

Ulberg was also involved with testing the algorithm alongside colleagues from the USGS. The System Testing and Performance Group generated dozens of earthquake simulations to ensure that GFAST would perform well. It took around 10 years to create and test GFAST before it was finally ready to be fully integrated into the ShakeAlert System.

The earthquake early warning alerts received by end-users will look exactly the same and the speed of earthquake detection will not change. The public will not notice a difference but will benefit from the improved event size accuracy and more comprehensive alerting regions.

There are several ways that Oregonians and Washingtonians can receive earthquake early warning alerts on their cell phones. Alerts can be delivered via texts from the Wireless Emergency Alert System, push notifications from the Android Operating System, and push notifications from free ShakeAlert-powered apps like MyShake. To ensure alert delivery, make sure that your phone’s operating system is updated and that Emergency Alerts are turned on in its settings. iPhone users should also turn on Local Awareness. Learn more from theUSGS website.

During an earthquake seconds matter! Immediate action can save lives. As soon as you feel shaking or receive an alert, protect yourself!

• DROP where you are onto your hands and knees. This position protects you from being knocked down and reduces your chances of being hit by falling or flying objects. >
• COVER your head and neck with both arms and hands and bend over to protect your vital organs. If a sturdy table or desk is nearby, crawl underneath it for shelter. If no shelter is nearby, crawl next to an interior wall away from windows, hanging objects, and tall furniture.
• HOLD ON to your shelter until shaking stops. Be prepared to move with it if it shifts. If you have no shelter, hold on to your head and neck with both arms and hands.

If you are near or on the coast, or in a tsunami prone area, follow evacuation routes to higher ground or inland as soon as you are able after the shaking stops. Remember, the earthquake itself is the warning that a tsunami may be coming.