Sleeping residents of California’s San Francisco Bay Area were rattled awake by a magnitude 4.3 earthquake in the early morning hours of September 22.
The earthquake struck 1.25 miles east-southeast of Berkeley, Calif., with shaking felt as far away as Salinas, about 100 miles to the south, and Chico, about 150 miles to the north. The temblor does not pose any tsunami threat, according to the Pacific Tsunami Warning Center.
The epicenter of the earthquake was about 4.7 miles deep, according to a preliminary report from the U.S. Geological Survey. The agency’s analysis is continuing, but experts have tentatively linked the event with 10 other smaller quakes that have rattled the region within the past month, mostly too weak for people to notice.
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The earthquake occurred near the Hayward fault line, which runs from the north side of San Francisco Bay to southeast of San Jose. The largest known earthquake on record in the area was a magnitude 6.8 event in 1868.
The earthquake scale is logarithmic, not linear, so the historic quake released more than 5,600 times more energy than this morning’s event. San Francisco’s deadly 1906 earthquake, by comparison, was at least a magnitude 7.7 event, which occurred along the San Andreas fault.
Because of its history, the Hayward fault is carefully watched by scientists who worry that the now densely populated region could see much more serious damage the next time a very strong earthquake strikes.