4.5 Magnitude Earthquake Felt In Bay Area

SAN FRANCISCO BAY AREA, CA — An earthquake with a preliminary magnitude reading of 4.5 was felt in the Bay Area shortly before 3:30 p.m.

The epicenter was Tres Pinos, east of Salinas, according to the United States Geological Survey Shake Map. It was felt from north of San Francisco to San Luis Obispo on the Central Coast, and east to the Sierra Nevada mountains.

The USGS Tectonic Summary cites the Calaveras Fault as the source of the shaking, noting, "The Calaveras Fault is a mostly right-lateral, strike-slip fault. The 2003 Working Group Report divided the fault into three segments. The northern segment of the Calaveras Fault is virtually locked and this segment of the fault creeps at a rate between 2 and 3 mm/yr. At the southern end of its central stretch it creeps at about 14 mm/yr dropping northward to about 6 mm/yr (0.24 inch/yr) of creep at its intersection with the Hayward Fault."

The fault creeps about 15 millimeters per year.

"Historically, the southern half of the central segment of the Calaveras Fault has been the most seismically active segment of the fault. It produced the M6.2 Morgan Hill earthquake in 1984 and a M6.2 earthquake in 1911."

If earthquakes make you nervous, the USGS concludes, "Because its rate of creep nearly matches the total fault slip rate, it is widely believed that this segment of the fault is not capable of an earthquake having a magnitude much larger than the 1984 Morgan Hill earthquake."

Tuesday's earthquake follows three smaller earthquakes last Saturday centered in the San Leandro area. The largest earthquake there measured 3.2.

There are no initial reports of injuries or damage.

Did you feel it?

You may report it to the USGS for tracking purposes.

Report your response to USGS Did You Feel It.

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