Magnitude 4.2 Earthquake Shakes Bay Area
A 4.2 magnitude earthquake shook the San Francisco Bay Area early on February 13. The tremor was felt across the region, but initial reports indicate no significant damage or injuries.
- The quake was the largest in a swarm of at least 21 tremors that struck the San Ramon area on the morning of February 13. This series of quakes is considered an "earthquake swarm," which involves multiple tremors in a short period without a single, large mainshock. - The epicenter was located about 4 kilometers southeast of San Ramon at a depth of 9.6 kilometers. Specifically, it was traced to the southern end of the Canyon Lakes Golf Course and Brewery, where some liquor bottles fell from shelves. - This seismic activity is centered along the northern part of the Calaveras Fault, a major and active fault line in the East Bay. The San Ramon region is prone to these types of swarms, with at least six similar events recorded since 1970. - While the 4.2 magnitude tremor was the strongest, it was preceded by a 3.8 magnitude quake about 30 minutes earlier. In the hours that followed, at least five aftershocks of magnitude 3.0 or higher were also recorded. - The USGS received over 4,900 reports from people who felt the main quake through its "Did You Feel It?" system, with reports coming from as far as Santa Rosa and Santa Cruz. - The shaking reached a maximum intensity of Level IV near the epicenter, which is strong enough to be felt by many and rattle objects but is not typically associated with significant damage. - As a precautionary measure, Bay Area Rapid Transit (BART) slowed trains to conduct safety inspections of its tracks and systems, causing delays of up to 20 minutes for morning commuters. - Following the swarm, the USGS forecasted a 22% chance of another earthquake of magnitude 3.0 or higher occurring in the same area.
