San Francisco and San Antonio Earthquakes 2011: Both Happen on Same Day

Two earthquakes in the United States have taken place on the same day Thursday.

The first one took place in Texas, the epicenter of the quake being near rural Karnes County, 47 miles southwest of San Antonio. The quake was a 4.8 magnitude, which was eye-opening because it was a record breaker.

The quake struck at 7:24 a.m. local time, and was the largest earthquake on record for the area, surpassing a magnitude-4.3 shock recorded in 1993, according to the U.S. Geological Survey.

USGS geophysicist Don Blakeman said that southern Texas has been experiencing small earthquakes since the 1970s, and that 14 quakes between 2.6 and 3.4 magnitudes have been recorded since 1982.

But Thursday morning's quake was significantly larger.

It is a bit unusual, he said.

Blakeman also said it is impossible to predict if there will be any aftershocks. The quake was both big enough to produce some small aftershocks and small enough that they wouldn't necessarily be expected.

The second one took place in California, the epicenter being two miles southeast of Berkeley near San Francisco. The quake was a 3.9 magnitude, causing a sharp jolt but no immediate signs of damages or injuries.

The quake struck at 2:31 p.m. local time and was at a depth of about 6.1 miles, according to the U.S. Geological Survey.

The quake was felt as a sharp jolt in the East Bay area, and across the bay in San Francisco. It came almost 22 years to the day after the Loma Prieta earthquake struck the Bay Area during the 1989 World Series.

The quake also came on the same day Californians took part in an annual earthquake preparedness drill at 10:20 a.m. Thursday. More than 8.5 million people signed up to participate in the 2011 Great California ShakeOut.