More than a million new earthquakes spotted in archival data

Every 3 minutes. This is the frequency with which an earthquake hit southern California from 2008 to 2017, according to a new study published in Science shows.

Scientists have discovered more than 1.6 million previously unknown earthquakes, mostly tiny, by extracting seismic records. These results, which constitute the most comprehensive catalog of earthquakes ever produced to date, reveal in detail how the flaws cross the Golden State and highlight the operation of an earthquake by triggering an earthquake. other.

"Having a better catalog of earthquakes is like having a better microscope," said Robert Skoumal, a geophysicist at the US Geological Survey in Menlo Park, Calif., Not involved in this study. "We are able to look more closely at the location of the defects, their breakdown and their interaction."

Small and numerous

Zachary Ross, a seismologist at the California Institute of Technology in Pasadena, and his collaborators were motivated by a principle of earthquake science: catalogs of earthquakes are still incomplete. This is because small earthquakes, many of which are too small to be felt, always hide below the detectability limit. And these little temblors are much more numerous than the animals that make the headlines.

"For every unit of magnitude you decrease, you get about 10 times more," Ross said.

Ross and his colleagues used data from more than 500 seismometers in the Southern California seismic network to dispel modest and previously unrecorded earthquakes.

They used a technique called the correspondence model, which uses seismic waveforms of known earthquakes as a model, and then looks for matches in nearby seismic data.

"The recorded jolt … will look almost the same," Ross said. "They all see the same rocks during their journey."

Noise

Ross and his team have gone through a decade of seismic records using more than 280,000 earthquakes as model events. They discovered more than 1.6 million new earthquakes with a magnitude less than 0.3. Such ground shocks can also be caused by construction-related vibrations, ocean waves and nearby aircraft, Ross said.

"We are basically at the noise level of instrumentation."

Using small differences in seismic wave arrival times of an earthquake, scientists have calculated the hypocenter of each new event. This information, along with the timing and magnitude of an earthquake, allowed Ross and his colleagues to develop detailed maps of earthquakes in southern California.

Video of Caltech

The new catalog on earthquakes does a much better job in tracing fault lines and revealing how earthquakes trigger others compared to older records, Ross said.

-Katherine Kornei (@katherinekornei), Independent Scientific Journalist

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