Tuesday’s earthquake in California likely not a ‘foreshock’ to larger one, expert says

An earthquake that rattled parts of the San Francisco Bay Area on Tuesday may lead to aftershocks that could last days or longer.

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 about the chances for additional aftershocks.

“It’s based on the scale of the magnitude, so it’s 67% of a magnitude 3 or above,” Blisniuk said. “As we get to magnitude 5, which is what we just felt, there’s a 2% chance.”

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.