A magnitude 4.2 earthquake occurred at 6:16 p.m. Friday roughly 3 miles northwest of Palomar Observatory, causing shaking across San Diego County and beyond, according to the U.S. Geological Survey.

According to the San Diego Union-Tribune, The temblor — which was initially reported to be 4.5 — began 9 miles beneath the earth’s surface and was generated by the Elsinore fault system.

“This happened on an unnamed, smaller fault that’s part of the Elsinore,” said San Diego State University seismologist Tom Rockwell. “It is beneath Palomar Mountain, in an area of granitic rock.

“An aftershock in the 3.0 range could occur and there will be several smaller aftershocks.” The USGS said online that seismic shaking occurred throughout most of Southern California, reaching as far northwest as the Santa Monica area of Los Angeles County and to the eastern side of the Salton Sea.

The shaking was noted in downtown San Diego, where the Padres were preparing for a 6:40 p.m. game against the Colorado Rockies at Petco Park.

A quake of this magnitude is not uncommon in Southern California. They occur regularly along the Brawley seismic zone near the Salton Sea. Quakes measuring 4.6 and 4.9 occurred nearly Brawley in 2020.