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2004 Livermore Swarm

Jan. 21, 2004:

A swarm is underway beneath the Livermore Valley. The swarm started at 5AM Sunday morning with an M3.0 and is continuing. As of the 10:00 AM PST, there have been 5 M>3 quakes, the largest of which has been a M3.5, and seismic networks operated by the USGS and UCB have located approximately 36 quakes of M1.2 and higher.

Swarms at this particular location are unusual, but we have observed previous earthquake activity with similar magnitudes near the location and at similar depths of the quakes in this swarm. In 1991 there were quakes (M3.8 and M3.3) that shook the area (within 6-10 km of the current events). In all likelihood this swarm will abate in a few days to weeks as have so many other swarms in the east SF Bay region (such as the 2003 Dublin swarm and the 2002 San Ramon swarm).

Review of the borehole strainmeter data does not show any obvious activity at the nanostrain level. The nearest sites are on Sunol Ridge above Sunol and at Mill Creek, above the Hayward/Calaveras split, and just south of Niles Canyon. USGS and UC Berkeley scientists are monitoring the activity.

Map of Livermore seismicity

A ShakeMap has been generated for the M3.5 event on Tuesday evening. Area residents are encouraged to submit felt reports on events in the sequence at the Did you feel it? Web site. Links for the largest events in the sequence are below:

Map showing the recent Livemore earthquakes in the context of historical seismicity.Steve Walter, USGS

Follow the links below to see maps of the current earthquakes, historical events, and other information on events in the area:

California Integrated Seismic Network

CGS USGS OES Caltech UC Berkeley