Saturday, November 30, 2013

[Geology2] Could Big Pacific Earthquakes Trigger One Here?

Could big Pacific earthquakes trigger one here?

October 10th, 2009, 6:00 am 

By Gary Robbins, San Diego Union-Tribune science writer-editor

The five big earthquakes that have occurred in the South Pacific over the past 10 days are causing some anxiety here, with readers asking whether the ruptures in that part of the "Ring of Fire" could set off a fault in Southern California.

The quakes include the 8.0 shaker near American Samoa on Sept. 29 that produced a tsunami that sent 6-inch wavelets gently rolling up the mouth of the Santa Ana River in Orange County, about 5,000 miles away.

We raised the issue with  Susan Hough, chief of the Pasadena office of the U.S. Geological Survey and author of the upcoming book "Predicting the Unpredictable: The Tumultuous Science of Earthquake Prediction." (It'll be published on Dec. 21 by Princeton University Press.)


Seismologist Sue Hough. Image courtesy of USGS/Caltech

"Regarding long-range triggering, my own educated opinion is that the answer is yes (it could happen)," Hough said by email. "Waves from a big earthquake travel all the way around the globe: it's impressive to see what they look like on seismometers.

"It is possible, and there is growing evidence to back it up, that these waves can shake up distant faults, and sometimes cause earthquakes.  But the probability that even a very large quake will trigger something big in any one distant place are very, very, very low.  Just look at the monster 2004 Sumatra earthquake — there's evidence that the rate of global large earthquakes increased over the months/years following it, but it wasn't like the entire planet suddenly lit up with huge quakes.  If a M9.2 doesn't trigger the Big One in California, that lessens the concern that anything serious will happen here after a much smaller M8."

And why can't scientists predict such earthquakes?

"I spend about 70,000 words answering that question," Hough says, referring to her upcoming book. "I guess the short answer is that we've never identified a reliable precursor that tells us that a big earthquake is imminent.  But not for lack of trying!"


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