An estimated 5.0-magnitude earthquake centered in northern Baja California shook the U.S.-Mexico border region about 100 miles east of San Diego on Tuesday.
There were no immediate reports of any injuries or damage, authorities said.
The quake struck at 2:41 p.m., the U.S. Geological Survey said.
It was centered 21 miles southeast of Calexico, a U.S. border city of more than 37,000 residents.
The big temblor was followed within minutes by three aftershocks that ranged in magnitude from 3.1 to 3.7.
"It started off with a little jolt, then a rumble," said Sgt. Mike Misteriel of the Imperial County Sheriff's Department. The aftershocks producing a rolling sensation, he said.
Southeastern California and Mexican border communities have been jolted for days by a continuing earthquake swarm that has included temblors of magnitude-5.4 on Feb. 8, a 5.1 and 5.0 on Feb. 11 and four between 4.0 and 4.4.
