A magnitude 6.1 earthquake occurred at 2:36 a.m. on Friday far off the coast of Ensenada, Mexico, producing shaking that was widely felt in San Diego County, says the U.S. Geological Survey and San Diego State University. The shaker, originally reported as a 6.3 shaker, was followed by a 4.7 aftershock.
"The quake happened beneath the seafloor in an area that was a subduction zone tens of millions of years ago," said SDSU seismologist Tom Rockwell. "This is a very old area of faulting. It still builds up some strain that releases as a quake every once in awhile."
Rockwell said that there is a roughly five percent chance that a larger quake will occur in the same region over the next 24 hours.
Friday's quake hit at a point 170 miles southwest of San Diego; it was too far away and too small to create a tsunami that could have affected this area, Rockwell says. However, the quake awakened many people across the county. The hypocenter was 6.3 miles beneath the seafloor, which is a common depth for a quake of that size.
Correction: Rockwell originally said the subduction zone was tens of millions of years old. We incorrectly said billions.
See quakes as they happen
Temblor off California coast is region's largest recent quake shown on the U.S. Geological Survey's real-time earthquake map.
The Associated Press contributed to this report.
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