‘Twisted’ San Andreas fault described

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Research on the structure of California’s San Andreas fault suggests a rupture might shake some places harder than current forecasts predict, seismologists say.

Researchers with the U.S. Geological Survey found the southern section of the fault isn’t vertical in most places, as previously thought, but rather twists in opposite directions along its length, ScienceNews.org reported.

“We now have a picture of a propeller-shaped San Andreas,” USGS geophysicist Gary Fuis said.

This unexpected shape could make the San Andreas, which has been locked and building up strain in some parts as the Pacific and North American plates try to move past each other, even more hazardous, the researchers said.

“The dipping geometry may allow for significantly larger earthquakes,” Roland Burgmann, a geophysicist at the University of California, Berkeley, said, explaining that tilted faults possess more surface area in a given depth, potentially releasing more energy when they break.

In its northern section the fault leans to the southwest, then as it snakes to the south it becomes vertical in the Mojave Desert.

Closer to Mexico, it dips to the northeast, cutting into Earth’s crust at an angle of 37 degrees near San Bernardino, Calif., the researchers said.

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