SAN DIEGO _ A magnitude 4.5 earthquake erupted at 3:07 p.m. on Sunday about 11 miles southeast of Ocotillo Wells, causing shaking across much of San Diego County on Mother's Day, according to the U.S. Geological Survey.
The quake began 6.2 miles below the earth's surface, a common depth for that area. It appears that the temblor started on the northwest end of the Superstition Mountain fault zone, San Diego State University seismologist Tom Rockwell said on Sunday afternoon.
The USGS says that shaking was felt in Santee, El Cajon, Escondido, Oceanside, Del Mar, Encinitas, Campo, Julian, Ramona, San Diego, Borrego Springs, Boulevard, Vista, Lakeside, Imperial Beach, Lemon Grove, National City and Carlsbad.
The quake also was notable because it occurred at the southeast end of a related fault that caused the 6.5 Borrego Mountain quake in 1968. That quake began one mile north of Ocotillo Wells.
"When the Borrego Mountain earthquake struck in 1968, it was the largest and most damaging quake to have hit Southern California since the Kern County earthquake, 16 years earlier," said the Southern California Earthquake Center website.
"It was felt as far away as Las Vegas, Fresno, and even Yosemite Valley. The quake caused damage across most of Southern California _ power lines were severed in San Diego County, plaster cracked in Los Angeles, and the Queen Mary, in drydock at Long Beach, rocked back and forth on its keel blocks for 5 minutes."
Sunday's temblor "is another moderate earthquake in the larger San Jacinto fault zone, and there is a 5% chance of a larger event within the next 24 hours." Rockwell said. "This also may be a fore shock. But it most likely won't be followed by a larger quake."
