By Alan Duke
updated 5:28 AM EDT, Mon August 27, 2012
Los Angeles (CNN)
-- "A swarm" of several hundred earthquakes, the strongest measuring a 5.5 magnitude, were centered east of San Diego near California's border with Mexico on Sunday afternoon but caused little damage, seismologists said.
Sunday's shaking in Southern California's Imperial Valley was the most activity recorded there since the 1970s, according to U.S. Geological Survey seismologist Lucy Jones.
"We are having a swarm," Jones said. "We expect thousands of events (like this) over several days."
In Brawley, the town closest to the center of the swarm, a Fire Department dispatcher said there were no reports of injuries so far. Brawley is about 100 miles east of San Diego and about 200 miles southeast of Los Angeles.