SAN FRANCISCO (Reuters) - Big earthquakes over the last 30 years have not triggered global chains of massive seismic activity, U.S. scientists reported on Monday.
But major quakes do trigger other big ones close by and smaller ones far away, researchers said.
The news is reassuring for California and other quake-prone areas wondering if the 9.0 earthquake which has done so much harm in Japan could hasten troubles outside the region.
U.S. Geological Survey and University of Texas at El Paso scientists looked at whether magnitude 7 and higher quakes were followed by magnitude 5 quakes and larger ones in other parts of the world.
"Based on the evidence we've seen in our research, we don't think that large, global earthquake clusters are anything more than coincidence," Tom Parsons, a USGS geophysicist and author of a study appearing in Nature Geoscience, said in a statement.
Big quakes were noted a distance of two times the length of the fault from a major shaking, although smaller quakes could be triggered at great distance, it said.
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(Reporting by Peter Henderson, Editing by Sandra Maler)