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We Knew of 180K Quakes in a Decade. That Was Way Off

Southern California has experienced 1.8M, though all the additional ones were small
By Kate Seamons,  Newser Staff
Posted Apr 19, 2019 7:40 AM CDT
This Feb. 14, 1994 file photo shows California State University, Northridge students walking past a parking structure at the Los Angeles campus that collapsed in the Jan. 17 earthquake.   (AP Photo/Mark J. Terrill, File)

(Newser) – It turns out the 180,000 earthquakes that have been recorded in Southern California over the last decade is a number that's off—by a lot. New research puts the number at 1.8 million, according to a study published Thursday in Science. All those additional ones were incredibly small, so much so that many of them had a magnitude of less than zero, reports NPR, which explains "the churning of the ocean, a passing car, or even the wind can feel a lot like a minor quake to the sensors that blanket seismically active parts of the US." In Southern California, there are about 400 of those sensors, and the researchers took their data and performed a more powerful analysis on it using computer processors to arrive at the new count. It's equivalent to one quake every three minutes over the 2008 to 2017 period.

National Geographic reports the previous count was almost complete for quakes above magnitude 1.7; now the same can be said for quakes of magnitude 0.3 and up. And there's real value in that: The new data will help scientists fill in some of the blanks on where earthquakes occur and the interplay of fault systems, and could specifically be useful in identifying blind faults or the foreshocks that precede a bigger quake. Still, the Los Angeles Times reports the achievement doesn't change scientists' view that pinpointing when and where the next big quake will strike probably isn't possible. And the data isn't perfect in one way: the Times notes it only exposed minuscule quakes in places where larger ones had occurred. The San Andreas fault, for instance, "has been unbelievably quiet," per lead author Zachary Ross. (Read more discoveries stories.)

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