From: Roger Greenway, ENN
Published October 3, 2012 05:14 AM

Large Earthquakes create more aftershocks and farther away than previously thought

New research by the University of California has produced significant new data on large earthquakes the related aftershocks that can occur nearby and in distant locations. The largest earthquake in 2012 a magnitude 8.6 temblor on April 11 centered in the East Indian Ocean off Sumatra, did little damage, but it triggered quakes around the world for at least a week, according to a new analysis by seismologists from the University of California, Berkeley, and the U.S. Geological Survey (USGS).

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The April 11 quake was unusually large — the 10th largest in the last 100 years — and, similar to a few other recent large quakes, triggered small quakes during the three hours it took for seismic waves to travel through Earth's crust.

The new study shows, however, that some faults weren't rattled enough by the seismic waves to fail immediately, but were primed to break up to six days later.

The findings are a warning to those living in seismically active regions worldwide that the risk from a large earthquake could persist — even on the opposite side of the globe — for more than a few hours, the experts said.

"Until now, we seismologists have always said, 'Don't worry about distant earthquakes triggering local quakes,'" said Roland Burgmann, professor of Earth and planetary science at UC Berkeley and coauthor of the study. "This study now says that, while it is very rare — it may only happen every few decades — it is a real possibility if the right kind of earthquake happens."

"We found a lot of big events around the world, including a 7.0 quake in Baja California and quakes in Indonesia and Japan, that created significant local shaking," Burgmann added. "If those quakes had been in an urban area, it could potentially have been disastrous."

Burgmann and Fred F. Pollitz, Ross S. Stein and Volkan Sevilgen of the USGS reported their results online in advance of publication in the journal Nature.

Map of the earth shows earthquakes triggered around the globe within a week of the April 2012 earthquake off the coast of Sumatra (white star)

Read more at University of California.

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