Large, distant quakes can trigger changes in the San Andreas Fault, new study finds

Wednesday, May 11, 2011
By Paul Martin

By Paul Rodgers
MercuryNews.com
05/11/2011

Distant earthquakes — even thousands of miles away — have far more impact on California’s San Andreas Fault than scientists previously realized, new research has found.
Large quakes such as the magnitude 9.1 event in Sumatra that triggered tsunami waves across the Indian Ocean in 2004 and the 8.8 quake in Chile last year caused parts of the San Andreas Fault deep underground to suddenly slip, setting off small tremors, according to a study released Tuesday by seismologists with the U.S. Geological Survey in Menlo Park.
There’s still no evidence that large quakes in one part of the world can set off large quakes right away on different faults thousands of miles away, said David Shelly, a USGS scientist.
But learning how deep sections of the San Andreas can react when they are hit with seismic waves is all part of unlocking the mysteries of how earthquakes work — a search that could one day help scientists predict quakes, he added.
“Big earthquakes are triggering an acceleration of the fault that can last for hours or days,” Shelly said. “You are triggering something that lasts longer than the seismic waves that are coming through. Over time, that can increase the stress on neighboring patches on the fault, which can generate tremors.”

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