Quake aftershock rattles border area

Residents living on the U.S.-Mexico border were shaken Sunday by a magnitude 4.6 earthquake, part of a cluster of moderate aftershocks stemming from the magnitude 7.2 quake that jolted Baja California a week ago, authorities said.

Sunday’s quake struck at 9:42 a.m. and was centered about 29 miles south southeast of Mexicali, the U.S. Geological Survey said. No damage or injuries have been reported. In a 19-hour period from about 5 p.m. Saturday through noon Sunday, automated seismographs registered at least 17 quakes of magnitude 3 or above with epicenters near Calexico or Mexicali, said Don Blakeman, a geophysicist at the USGS’s National Earthquake Information Center in Golden, Colo.

“It’s pretty much expected that after a large, shallow main shock there is almost always going to be a busy series of aftershocks,” Blakeman said. “We sometimes see these go on for weeks or even months, but as time goes by the aftershocks get smaller and less frequent.”

Aftershocks from the 7.2 earthquake have been recorded as far north as Santa Monica Bay off the coast of Malibu. The April 4 quake killed two people and injured more than 230 others. Centered 30 miles south of the border, it caused 45 buildings in Baja to collapse or partly collapse, authorities said.