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Tuesday’s earthquake in California might be ‘foreshock’ to larger one, expert says
An earthquake that rattled parts of the San Francisco Bay Area may have been the precursor to a larger one that could happen in the coming days.
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SAN JOSE, Calif. – An earthquake that rattled parts of the San Francisco Bay Area may have been the precursor to a larger one that could happen in the coming days.
The magnitude 5.1 earthquake struck shortly before noon just southeast of San Jose, near Alum Rock. It was widely felt across the Bay Area. People as far away as San Diego and Lake Tahoe reported shaking.
A few hours after the temblor, FOX Weather spoke to Kimberly Blisniuk, Ph.D., an earthquake geologist at San Jose State University.
"There’s a 67% chance that a bigger, mainshock will occur within the next week," Blisniuk said, noting that number reflects the forecast for a magnitude 3 or above. "So, what we felt may have been a foreshock to a larger earthquake."
"As we get to magnitude 5, which is what we just felt, there’s a 2% chance," she added.
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As of Wednesday morning, the U.S. Geological Survey forecast for a magnitude 3 or greater quake was at 21% within a day and 45% within a week. The forecast for an earthquake larger than a magnitude 5 or greater was less than 1%.
There have been at least three other tremors reported in the area where Tuesday’s shaking happened, ranging from 2.7 to 3.5 in magnitude.
Blisniuk said Tuesday’s tremor happened along the Hayward-Calaveras fault, which is part of the larger San Andreas fault system.
"These faults are basically accommodating motion between two big tectonic plates," Blisniuk said. "The two plates are the North American Plate and the Pacific Plate."
According to the USGS, the Calaveras fault last produced a notable earthquake in October 2007. That was a 5.4-magnitude temblor near Alum Rock.
California experiences two or three earthquakes each year that can cause sizable damage and register a magnitude of 5.5 and higher, according to the National Earthquake Information Center.