The U.S. Geological Survey says the quake hit at 8:19 p.m. local time Friday and was centered 11 miles from Ridgecrest, where a magnitude 6.4 quake struck Thursday. The agency initially said the earthquake had a magnitude of 7.1.
The quake was felt downtown as a rolling motion that seemed to last at least a half-minute. It was felt as far away as Las Vegas, and the USGS says it also was felt in Mexico.
If the preliminary magnitude is correct, it would be the largest Southern California quake in 20 years.
Meanwhile, seismologists say there have been 1,700 aftershocks in the wake of Thursday’s quake.
A magnitude 5.4 quake at 4:07 a.m. Friday is so far the strongest aftershock of Thursday’s 6.4 quake, which struck in the Mojave Desert near the town of Ridgecrest.
Zachary Ross of the California Institute of Technology says the number of aftershocks might be slightly higher than average. He also says a quake of that size could continue producing aftershocks for years.