Though large earthquakes are said to not be increasing, everyone is now predicting them

December 22, 2011 – OREGON – Since the magnitude 9.1 earthquake in Sumatra in 2004, five more giant earthquakes have struck the continents ringing the Pacific Ocean. And some experts speculate that the planet has entered a period of increased seismic activity that could trigger giant earthquakes in vulnerable regions including the Pacific Northwest. A somewhat reassuring new study suggests otherwise. University of California researchers examined the timing of earthquakes worldwide from 1900 and found no evidence of a domino effect in which one great earthquake triggers others on distant continents. It could be random chance. ‘We don’t want people to assume that our conclusion means the ongoing risk is small,” says study co-author Peter Shearer, a professor of geophysics at the University of California San Diego. “There is a significant risk of big earthquakes in all subduction zones.” It’s just that the run of very large earthquakes most likely does nothing to change the risk in distant locations, Shearer says. But the data is less than convincing to some experts, who think it’s possible that short-term risk of a great earthquake has increased in the Northwest.  “There is a possibility that maybe we should be worried about this,” says Oregon State University geologist Chris Goldfinger. “I definitely do not dismiss it.” Thorne Lay, a professor of geophysics at the University of California Santa Cruz, says scientists don’t understand the physical processes well enough to rule out long-distance triggering of great earthquakes based on observations to date. “One would really need to have good data in the location of each great event to see whether earlier remote large events had changed earthquake timing locally,” he says. “Unfortunately, careful work has not been done in all regions of recent big events or the data are very poor due to lack of nearby seismic networks.” The likelihood that a magnitude-9 earthquake will hit the Northwest within 50 years is about 10 to 15 percent, according to the most widely cited estimate. From Northern California to British Columbia, an ocean-spanning slab called the Juan de Fuca Plate is pushing beneath the North American plate in the Cascadia subduction zone. Geologists have found evidence of 19 massive earthquakes on this fault in the past 10,000 years. The most recent struck in 1700. It drove a 30-foot wall of water over low-lying coastal areas. The tsunami crossed the Pacific and flattened houses along Japan’s east coast. Global records since 1900 show a cluster of very large earthquakes between 1950 and 1965 followed by 38-year pause in magnitude 8.5 or greater events until the surge that began in 2004. There was the 9.1 to 9.3 magnitude earthquake in the Indian Ocean in 2004, a 8.8 in Chile in 2010 and a 9.0 magnitude earthquake in Japan in 2011- all of which shifted the planet on its axis. Is this mere coincidence? The number of events in both clusters was too few to stand out as more than random variation, Shearer and co-author Philip Stark conclude in a paper published in the Proceedings of the National Academy of Sciences. –Oregon Live  – edit added

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