US earthquakes actually a powerful Siberian quake

by Brian Fisher Johnson
Thursday, January 5, 2012

A powerful earthquake struck Siberia Monday - but U.S. seismic stations interpreted its signals as originating closer to home. USGS Earthquake Hazards Program

A magnitude-7.3 earthquake in Siberia Monday was mistaken by U.S. seismometers as temblors in Idaho and California.

The actual quake occurred about 500 kilometers deep, in the Sea of Okhotsk about 315 kilometers northwest of Russia’s Kamchatka Peninsula, the U.S. Geological Survey reported.

Automated seismic centers in the western United States registered the resulting waves as originating from a magnitude-4.8 quake in southeastern Idaho, a magnitude-3.8 earthquake in Central California and a magnitude-3.4 earthquake in Southern California, according to the Associated Press; the reports were tagged with warnings that they had not been reviewed by seismologists.

That said, seismologists quickly recognized that the readings were false. The phenomenon is not uncommon, says John Bellini, a geophysicist at the National Earthquake Information Center in Golden, Colo.

“Just about any large earthquake like this will give off all sorts of reflections [in the Earth’s interior] that create small 'earthquakes' in other places,” Bellini says. “You just ignore it, pretty much.”

Bellini says the depth of the quake’s epicenter may have been the reason why U.S. seismic stations identified the signal as a nearby earthquake, as opposed to background noise.

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