Deep underground forces explain quakes on San Andreas Fault

[Jim__]

From phys.org:

Rock-melting forces occurring much deeper in the Earth than previously understood appear to drive tremors along a notorious segment of California's San Andreas Fault, according to new USC research that helps explain how quakes happen.

The study from the emergent field of earthquake physics looks at temblor mechanics from the bottom up, rather than from the top down, with a focus on underground rocks, friction and fluids. On the segment of the San Andreas Fault near Parkfield, Calif., underground excitations—beyond the depths where quakes are typically monitored—lead to instability that ruptures in a quake.

"Most of California seismicity originates from the first 10 miles of the crust, but some tremors on the San Andreas Fault take place much deeper," said Sylvain Barbot, assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences. "Why and how this happens is largely unknown. We show that a deep section of the San Andreas Fault breaks frequently and melts the host rocks, generating these anomalous seismic waves."The newly published study appears in Science Advances. Barbot, the corresponding author, collaborated with Lifeng Wang of the China Earthquake Administration in China.

The findings are significant because they help advance the long-term goal of understanding how and where earthquakes are likely to occur, along with the forces that trigger temblors. Better scientific understanding helps inform building codes, public policy and emergency preparedness in quake-ridden areas like California. The findings may also be important in engineering applications where the temperature of rocks is changed rapidly, such as by hydraulic fracturing.

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