A magnitude-4.0 earthquake shook large parts of San Bernardino and Riverside counties early Monday, but there were no immediate reports of injuries or damage.

The temblor, which struck around 7:15 a.m., was centered 2 miles east of Loma Linda in San Bernardino County and occurred at a depth of 6 miles, according to the U.S. Geological Survey.

The main shock was preceded by a pair of magnitude-2.6 foreshocks including one that hit 10 minutes earlier, California Institute of Technology seismologist Kate Hutton said.

"It was felt pretty much throughout the Inland Empire," Hutton said, referring to the fast-growing region east of Los Angeles that includes San Bernardino and Riverside counties.

Hutton said it was too early to pin down which fault the quake occurred on. But she said the quake was close to the San Jacinto Fault, an active offshoot of the San Andreas Fault.

The San Bernardino County Sheriff's Department had not received reports of injuries or damage, dispatch supervisor Shelby White said.

The epicenter was in Loma Linda, which has a population of 21,000 and is home to Loma Linda University and Medical Center.