Geologists Make Headway on Earthquake Warning Systems

Rescue workers and volunteers search a building that collapsed after an earthquake in downtown Mexico City, Tuesday, Sept. 19, 2017. (AP Photo/Rebecca Blackwell)

(CN) – A new satellite-based early warning system could provide accurate information on the size and epicenter of an earthquake moments after it initially occurs, which similar tools often cannot capture.

The system, called G-FAST, examines ground motion data measured by Global Navigation Satellite Systems (GNSS) to project the magnitude and origin of powerful earthquakes magnitude 8 and larger. These massive quakes often occur at subducting plate boundaries, where one plate thrusts beneath another like off the coast of Chile and the U.S. Pacific Northwest.

Using data collected by Chile’s more than 150 GNSS stations, a team of researchers tested G-FAST’s accuracy against three large megathrust earthquakes that occurred in the nation: the 2015 magnitude 8.3 Illapel, the 2014 magnitude 8.2 Iquique, and the 2010 magnitude 8.8 Maule quakes. The results were published Tuesday in the journal Seismological Research Letters.

Led by Brendan Crowell of the University of Washington, the team found that G-FAST was able to supply size estimates that were within 0.3 units of the known magnitudes in 45 to 60 seconds after their origin. The system also provided estimates of the epicenter and fault slip that accurately reflected the actual measurements within 60 to 90 seconds after each quake began.

“We were surprised at how fast G-FAST was able to converge to the correct answers and how accurately we were able to characterize all three earthquakes,” said Crowell, who is also a research scientist with the Pacific Northwest Seismic Network.

Most early warning modules measure seismic-wave properties to quickly describe an earthquake. However, these systems often cannot collect enough data to determine how a large quake will grow, which can lead to seismologists underestimating its magnitude. That problem can be avoided with satellite-based systems like G-FAST.

It is challenging to test such early warning systems because magnitude 8+ earthquakes are fairly rare, Crowell noted.

“We decided to look at the Chilean earthquakes because they included several greater than magnitude 8 earthquakes, recorded with an excellent and consistent GNSS network,” he said. “In doing so, we would be able to better categorize the strengths and weaknesses in G-FAST.”

The tests will play a role in developing G-FAST for use in the United States, where the team has been trying to include it in a prototype early warning system known as ShakeAlert operating in Washington state, Oregon and California. The Chilean earthquakes comprise roughly half of the magnitude 8 events in the recorded catalog of quakes that are used to test G-FAST and other geodetic algorithms for inclusion in ShakeAlert, Crowell said.

Ten magnitude 8 or larger earthquakes have occurred along Chile’s coast over the past century. Of those, the magnitude 9.5 Valdivia quake in 1960 is the largest in recorded history.

“The hazard due to these large events is well recognized and understood,” in Chile, University of Chile researcher Sergio Eduardo Barrientos writes in a separate paper published this week in Seismological Research Letters. “Return periods for magnitude 8 and above events are of the order of 80 to 130 years for any given region in Chile, but about a dozen years when the country is considered as a whole.”

Following the 2010 Maule earthquake, the nation began installing a network of digital broadband seismic and ground motion stations, GNSS stations, and GPS stations to supply accurate information for damage assessment and tsunami warnings.

Since 2012, the Centro Sismologico Nacional at the University of Chile has operated more than 100 stations, and recently started managing nearly 300 strong-motion accelerometers that measure ground shaking.

In a third study, also published Monday in Seismological Research Letters, researchers present results from a review of new improvements made to Mexico’s early warning system, SASMEX.

The warning module gave Mexico City’s residents almost two minutes of warning prior to the 2017 Tehuantepec earthquake, which was centered off the southern coast of the nation. At magnitude 8.2, it is the largest quake detected by the system.

SAMSEX also sent an alert for the magnitude 7.1 Morelos earthquake that occurred nearly two weeks after the Tehuantepec quake. However, the Morelos quake was centered much closer to Mexico City, allowing only a few seconds of warning prior to the start of shaking.

 

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