Parts of Southland shaken by a 4.9 earthquake on a dangerous fault near Anza

Parts of Southern California were shaken hard Friday evening by a 4.9 earthquake that struck near Anza in Riverside County. It was felt especially strongly in San Diego County.

The quake erupted along the San Jacinto fault system, which scientists say is capable of producing a 7.3 to 7.5 temblor.

The shaker also was felt in downtown Los Angeles, other areas of L.A. county and the Inland Empire.

The quake hit at 6:53 p.m. at a spot near the San Diego-Riverside county line, 11 miles east-southeast of Anza and 16 miles north-northeast of Warner Springs, at a depth of 6.6 miles.

It’s common for quakes to occur to depths of 10 miles in Southern California.

“This was a moderate earthquake in an area that has produced a lot of moderate earthquakes,” said Tom Rockwell, a San Diego State University scientist who has studied the San Jacinto system for years.

“This is a section of the fault where we expect larger quakes. The last big one occurred on Nov. 22, 1800, when we had a 7.3 earthquake. It produced up to 13 feet of lateral displacement near Anza.”

The average return time of a big quake in that area is 270 years.

“Could we have a big one tomorrow? Yes,” Rockwell said. “Could it wait another 100 years? Yes. The return time is quite variable.

“There is a 5% chance that this was a foreshock to a larger earthquake in the next 48 hours. But there’s a 95% chance that nothing will happen.”

Significant aftershocks to Friday’s quake were expected.

Robbins writes for the San Diego Union-Tribune.