Sensors misread Russian quake as local

It was a little like the scene in “The Empire Strikes Back” when C-3PO tells R2-D2, “You know better than to trust a strange computer!”

Computerized sensors in California detected what appeared to be a couple of small regional earthquakes early Monday morning, but seismologists quickly realized the computers had picked up waves rippling out from an earthquake near Russia.

“It happens with a particular circumstance, when there’s an earthquake that’s far away that’s very deep,” said Kate Hutton, a seismologist whose lab at Caltech works with the U.S. Geological Survey to detect quakes.

“Our computer was briefly confused,” she said.

The real earthquake was a magnitude 7.3 temblor in the Sea of Okhotsk. It occurred about 1 a.m. Pacific Standard Time, about 300 miles below ground. Shortly after, sensors in the U.S. sent out alerts of a magnitude 3.4 earthquake in Big Bear, a 3.8 quake in Central California, and a 4.8 quake in southeastern Idaho, according to the Associated Press.

Officials at the U.S. Geological Survey’s National Earthquake Information Center deleted the reports within minutes and said Monday afternoon they could not confirm the exact details.

Computers get confused about local quakes about three times a year, said geophysicist Bruce Presgrave of the Geological Survey.

“We’re betting on the usefulness of very fast locations for, say, a magnitude 7 earthquake in Southern California and kind of accepting the fact that we do occasionally have to live with bogus events,” he said.

Big, deep, distant earthquakes and modest local quakes send a similar number of vibrations per second through the earth, Presgrave said. But seismologists can distinguish the two by looking at the shape of the waves. Also, the sensors detected the vibrations in California at the time a seismic wave moving out from Russia would be expected to arrive.

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jia-rui.chong@latimes.com