The Alum Rock Earthquake of October 30, 2007, 08:04 pm PDT

A strong earthquake shook the Bay area at 08:04 pm PDT on October 30, 2007 (03:04 UTC on October 31, 2007). Its was located about 8 miles NNE of Alum Rock, CA at depth of 6 miles on the Calaveras Fault. According to researchers at the Berkeley Seismological Laboratory the earthquake had a moment magnitude of 5.4 (Figure 1). The event led to strong shaking in the epicentral region (Figure 2). Felt reports were entered from beyond Santa Rosa to the NW, the Sierras to the E and King City to the S (Figure 3).

The earthquake occured on the Calaveras fault. During this earthquake the fault ruptured for about 3 miles toward the SE from the hypocenter. This kind of movement is typical for earthquakes in our region.

Figure 1: Moment tensor results for the Alum Rock earthquake of October 30, 2007. For this solution, stations from more than 50 km (30 miles) were used. The fits are very good and the mechanism is consistent with the right lateral movement along the Calaveras Fault.

Figure 2: Shakemap intensity map for the Alum Rock earthquake of October 30, 2007. Note that the shaking was strong in the epicentral region. There is some evidence of rupture directivity. Shaking was felt throughout the Bay Area and the Central California region of the Central Valley.

Figure 3: Community Internet Intensity Map for the October 30, 2007, Alum Rock earthquake. This assessment of shaking in each area is compiled from internet reports of the residents. People who felt the earthquake are encouraged to report their observations on the web by pointing their browsers to

http://pasadena.wr.usgs.gov/shake/STORE/X40204628/ciim_form.html

The Berkeley Seismological Laboratory at the University of California has been monitoring the seismic activity in Northern California since 1886. Together with the United States Geological Survey (USGS) and the California Institute of Technology (Caltech) in Pasadena, Berkeley currently operates the California Integrated Seismic Network.