SAN DIEGO (CNS) - Four aftershocks shook the Imperial Valley and eastern San Diego County within a half hour, according to automated seismographs and computers operated by the U.S. Geological Survey.
The largest temblor, magnitude 4.1, hit at 3:35 p.m. Its epicenter was about 40 miles south of Mexicali, or about 120 miles east-southeast of San Diego.
It was preceded by a 3.2 magnitude quake at 3:02, and a 2.8 shaker at 3:11 in the same location. All three were strong enough to be felt in East County.
In the midst of that swarm, a magnitude 2.5 quake struck just north of the U.S-Mexico border. It hit at 3:18 and was epicentered 3 miles south-southeast of Ocotillo, a small cluster of homes on the San Diego-Imperial county line 95 miles east of San Diego.
The San Diego County sheriff's office said they had no reports of injury or damage.
Thousands of similarly-sized aftershocks have rattled the area since a magnitude 7.2 earthquake struck April 2, killing two people in Mexicali and severely damaging canals, schools and older buildings in Imperial County.