The science behind California’s two big earthquakes

While earthquakes are not unexpected, the two most recent temblors are the largest that have struck this area in decades. And they promise to yield fresh clues about its complex geology.

The duo of quakes struck in what’s known as the Eastern California shear zone—an area east of the infamous San Andreas fault, where the Pacific Plate grinds against the North American Plate, creeping northwest at roughly two inches each year. The area extends from the southern Mojave Desert, up the eastern side of the Sierra Nevada, and into western Nevada. It’s crisscrossed by fractures in the Earth caused by the movement along the nearby tectonic plate boundary.

“The Eastern California shear zone is a really interesting area,” says Wendy Bohon, an earthquake geologist at the Incorporated Research Institutions for Seismology (IRIS). “How is it working? How is it accommodating plate motion? What are going to be the big structures that come out of this millions of years down the road?”

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