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

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 like 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.”

The research was published this week in the journal Nature Geoscience.

Read more : http://www.mercurynews.com/science/ci_18035659?nclick_check=1

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