A magnitude 4.2 earthquake jolted Los Angeles early Thursday, followed quickly by a series of aftershocks, but there were no reports of any damage or injuries.

The main temblor struck at 4:29 a.m. at a depth of 4.3 miles, its epicenter 1.4 miles north of the city of San Fernando, according to the U.S. Geological Survey. To San Fernando Valley residents, the quake was felt as a sharp jolt.

The quake was initially registered as a magnitude 4.3 quake but downgraded about 10 minutes later by the USGS. It was almost immediately followed by a magnitude 3.3 aftershock, which some San Fernando valley residents did not feel. But a sharp aftershock initially measured at 3.9 — later lowered to 3.8 — hit at 6:48 a.m. and was felt where the second had not been.

The earthquake occurred in the Sierra Madre Fault Zone, said Paul Caruso of the USGS.

By late morning, more than 60 aftershocks had been detected, the largest measuring a magnitude of 3.8, Caltech seismologist Jen Andrews said. Andrews said the temblor is not surprising, given the array of fault zones in the area. She noted that Thursday morning’s shaker occurred at the intersection of faults responsible for the 1971 San Fernando earthquake and the 1994 Northridge quake, but there was no way to draw any connection with those events.

USGS seismologist Susan Hough said initial modeling indicates that more smaller aftershocks can be expected in the area, and there’s a roughly one-in-10 chance of a quake measuring 4.2 or larger occurring over the next month.

Hough said more than 50,000 people reported feeling the shaking on the USGS’ “Did You Feel It” web page.

People in the San Fernando Valley, La Crescenta, downtown Los Angeles, the Miracle Mile area, Hollywood and Pasadena reported feeling the first quake, which was also felt in Orange County.

The Los Angeles Fire Department said it immediately implemented its post-earthquake protocols, with fire department vehicles and helicopters patrolling the department’s 470 square-mile jurisdiction to look for damages or residents experiencing emergencies. About 5:30 a.m., the department said it had completed its protocols.

“The LAFD has concluded the systematic survey of the City of Los Angeles by ground and air, and is pleased to report that no major infrastructure damage was noted by our personnel in the City of Los Angeles, and that there has been no loss of life or serious injury that we can directly attribute to the (magnitude) 4.2 earthquake,” spokesman Nicholas Prange said.

The Los Angeles and Beverly Hills police departments reported normal operations, but officers at both strongly encouraged residents to be prepared in the event of a major earthquake.

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