As hundreds of small quakes hit in the Imperial Valley of California Sunday and Monday, another series of earthquakes occurred in the floor of the Gulf of California, south of Puerto Peñasco, Sonora.
Two of those that hit near Rocky Point, as the Sonoran beach town is known, were strong enough to be felt, but not rough enough to cause any damage.
On Sunday night at about 10:20, a quake registering 5.3 on the Richter scale happened about 70 miles south-southwest of Rocky Point.
About 3:30 Monday afternoon, a 5.0-magnitude quake occurred, centered about 50 miles south of Puerto Peñasco.
Mike Riggs, owner of Latitude 31 Sports Bar and Grill in Rocky Point, said he felt the Sunday night quake.
"The bed started shaking and the kids got up," Riggs said. "We got up and we all went outside. It was something exciting."
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Riggs was filling out an online report about the Sunday-night quake while sitting at his bar Monday afternoon when another earthquake hit.
"This one was kind of like a big jerk," Riggs said.
While Riggs felt both quakes, Rosie Glover, who runs an insurance business in the town, didn't feel either of them, she said.
While no notable damage occurred in Peñasco, that was not the case around Brawley, Calif., where hundreds of earthquakes hit on Sunday and Monday, the largest registering at 5.5 and 5.3.
The quakes shattered windows, knocked trailer homes off their foundations and put people in the small farming town 75 miles west of Yuma on edge.
No injuries were reported in the region, which has a long history of such earthquake swarms.
"The type of activity that we're seeing could possibly continue for several hours or even days," said U.S. Geological Survey geophysicist Robert Graves.
The seismic activity is not unusual, but scientists have puzzled over the cause.
The last significant swarm occurred in 2005 when a thousand quakes, the largest at magnitude-5.1, shook the south shore of the Salton Sea in California.
In 1981, a cluster of quakes hit a region five miles to the northwest of Sunday's sequence, with the largest measuring a magnitude-5.8. The region was very active in the 1960s and 1970s.
"They seem to light up and turn off for reasons we don't understand," said USGS seismologist Susan Hough.
The Associated Press and Arizona Daily Star reporter Tim Steller contributed to this report.
