A moderate earthquake shook a wide area of Southern California on Monday, according to the U.S. Geological Survey.
The temblor struck at 9:55 a.m. PT in a remote, mountainous area northeast of San Diego and was estimated to be magnitude 4.7 (earlier reports gave it a magnitude of 5.1). The quake's center was 16 miles south of Palm Desert, Calif. There were no initial reports of damage or injuries.
Several smaller seismic events were also reported around the same time.
According to Leslie Gordon of the USGS, the initial magnitude reports are generated by computer and automatically sent out. Those reports are revised after data are reviewed by USGS seismologists.
The quake was "a little tricky to analyze" because of a small quake that preceded the larger event, said USGS seismologist Susan Hough. That threw off some of the instruments, she said, and so the depth of the quake as well as its precise epicenter and relation to known faults in the area remained unclear.
The quake was felt sharply in the local area, The Associated Press reported, and also rolled through downtown Los Angeles, San Diego and Orange County.
Some Twitter users reported that they slept through the quake, while other reported being startled awake.
Kristen Nicole (@KristenNicole25) tweeted: "Apparently there was an #earthquake in #SoCal this morning. People said they felt it in #LA... Not this girl."
Twitter user Anayeli (@iamanayeli) reported the quake woke her up in Riverside. "At least I won't be late for class!," she wrote.
Terry Raposa said on her Facebook account that she felt the quake in Lake Elsinore.
"Slam and then felt sea sick! LOL!," she wrote, NBCLosAngeles.com reported.
NBCLosAngeles.com and The Associated Press contributed to this report.