LOS ANGELES (CBS) — A 6.3-magnitude quake struck 163 miles southwest of Avalon Friday morning.

The temblor occurred at 2:36 a.m., according to the USGS.

“This event is located some 400-450 km west-southwest of the plate boundary between the Pacific and North America plates – the San Andreas fault system in Southern California – and is not associated with that fault system,” the agency said in its tectonic summary.

The quake – which was reportedly felt as far south as Mexico – was followed by a magnitude 4.7 aftershock.

There were no reports of injuries or damage.

Cal Tech seismologist Anthony Guarino told KNX 1070 NEWSRADIO that an offshore quake of this magnitude is “very unusual”.

“We don’t usually have quakes this size offshore, the largest we’ve had offshore is approaching maybe a five [magnitude],” Guarino said.

No tsunami warning was issued because there was no “significant uplift of the ocean floor” detected following the quake, according to Guarino.

Monica in Encinitas said the temblor jolted her from her bed.

“Compared to most earthquakes that I feel down here, it was very short, but it was pretty violent,” she said.