LOS ANGELES - Seismologist Lucy Jones said Friday night's 7.1-magnitude earthquake was the "main event" -- and aftershocks in Southern California in the days, months and even years ahead were possible.
"The largest aftershock, on average to a 7.1 (magnitude), would be about a magnitude 6.0. So another magnitude 6.0 similar to yesterday's earthquake in size would be not surprising to anybody," Jones said.
Friday night's quake was the largest temblor in the region in 20 years. It was initially reported as magnitude 7.1, downgraded and then upgraded back to 7.1 by the U.S. Geological Survey.
The quake was reported at 8:19 p.m. and was centered 11 miles from Ridgecrest, a Mojave Desert town about 150 miles away from Los Angeles, the same area where a 6.4-magnitude earthquake struck on the Fourth of July. Building damage, fires and several injuries were reported from the earlier quake.
Jones called Thursday's earthquake a "foreshock," meaning an earthquake preceding a larger one. She added that the Friday quake was part of the sequence that produced the earlier quake on July 4.
There was about a 15-mile difference between the epicenter of the Thursday and Friday earthquakes, Jones said. The seismologist added that Caltech was on a call with the USGS and California Geological Survey when the quake hit.
Friday night's jolt was felt in downtown Los Angeles as a rolling motion that seemed to last at least a half-minute.
Reports said the quake rocked chandeliers and rattled furniture as far away as Las Vegas, and the U.S. Geological Survey said it was felt in Mexico as well.
The Associated Press contributed to this report.