MENLO PARK - A major, magnitude 7.4 earthquake that occurred this morning deep below the Marianas Islands in the South Pacific trigged a series of false earthquake reports in the Bay Area minutes later, the U.S. Geological Survey says.

Seismologist David Oppenheimer, who heads the San Francisco Bay Area Earthquake Project, said the high frequency vibrations from the giant quake were so strong that the 430 quake automated reporting stations in Northern California interpreted the shock waves as caused by a local earthquake.

Each station transmitted its findings to an automated software system in Menlo Park called an "automator." There were so many reports from so many stations that the software assumed there was more than one quake, Oppenheimer said. By the time the shaking eased, the software had created six false quakes at various locations in the Bay Area from Marin to the Peninsula to the East Bay with magnitudes ranging from magnitude 3.8 to 4.2.

The false reports were posted automatically on the USGS Web site and at least some of the 110,000 people who signed up for earthquake notification by cell phone were called. The quake was also picked up and interpreted as local by the same software in Southern California, which reported a false quake there, Oppenheimer said.

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