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Following two earthquakes, the searching for hidden tremors continues in Southern California

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Ten times more earthquakes now detected in Southern California. The richer data set will allow scientists to gain a clearer picture of how seismic events affect the region

A house is left damaged by an earthquake, triggered by a previous day quake, near the epicenter in Trona, California

Two powerful earthquakes struck Southern California, causing concern over a large area already from Las Vegas to Sacramento to Los Angeles to Mexico, rattling nerves and disrupting plans on a holiday weekend. There were no reports of fatalities and no severe damage to infrastructure, but questions on how earthquake science has progressed have been raised.

Leer en español: Luego de dos terremotos, la búsqueda de temblores ocultos continúa en el sur de California

A group of scientists developed a technique to reliably record all earthquakes down to a magnitude of 0.29 on the Richter Scale, whereas previous methods, only allowed earthquakes larger than size 1.7 to be reliably recovered.

"Earthquakes follow a well-known power-law size relation, with smaller events occurring much more often than larger events. Earthquake catalogs are thus dominated by small earthquakes yet are still missing a much larger number of even smaller events because of signal fidelity issues. To overcome these limitations, we applied a template-matching detection technique to the entire waveform archive of the regional seismic network in Southern California," the researchers reported.

Template matching is a technique in which slightly more massive and more easily identifiable earthquakes are used as templates to illustrate what an earthquake's signal at a given location should look like. When a likely candidate with the matching waveform was identified, the researchers then scanned records from nearby seismometers to see whether the earthquake's signal had been recorded elsewhere and could be independently verified.

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"This effort resulted in a catalog with 1.81 million earthquakes, a 10-fold increase, which provides important insights into the geometry of fault zones at depth, foreshock behavior and nucleation processes, and earthquake-triggering mechanisms. The rich detail resolved in this type of catalog will facilitate the next generation of analyses of earthquakes and faults," the scientists added.

The new data reveals that there are about 495 earthquakes daily across Southern California occurring at an average of roughly three minutes apart. Previous earthquake cataloging had suggested that approximately 30 minutes would elapse between seismic events.

"It's not that we didn't know these small earthquakes were occurring. The problem is that they can be challenging to spot amid all of the noise," Zachary Ross, lead author of the study, stated.

Ross collaborated with Egill Hauksson, a research professor of geophysics at Caltech, as well as Daniel Trugman of Los Alamos National Laboratory and Peter Shearer of Scripps Institution of Oceanography at UC San Diego.

"The findings were worth the effort," Hauksson said. "Seismicity along one fault affects faults and quakes around it, and this newly fleshed-out picture of seismicity in Southern California will give us new insights into how that works," Hauksson added. The expanded earthquake catalog reveals previously undetected foreshocks that precede significant earthquakes as well as the evolution of swarms of earthquakes. "The richer data set will allow scientists to gain a clearer picture of how seismic events affect and move through the region," Ross concluded.

 

Latin American Post Staff

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