An earthquake of magnitude 4.0 rattled the Bay Area shortly after 6 A.M. local time on November 26—the quake is the largest so far in a string of recent activity near Gilroy, Calif.
The U.S. Geological Survey had originally estimated the earthquake to be magnitude 4.3 but quickly revised the strength down to 4.0. That kind of revision is typical in the immediate aftermath of a quake as scientists analyze the data available to them.
The earthquake’s epicenter was 1.7 miles deep and about five miles east of Gilroy, south of San Francisco Bay and located about halfway between San Jose and Salinas, inland from the coast. The National Tsunami Warning Center quickly determined that the event did not pose any threat of a tsunami.
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The quake is the latest in a string of geological activity located in the area; USGS has identified 10 tremors in recent weeks that might be connected to this largest-yet event. The prior temblors were predominantly weaker than magnitude 2.0, which people usually do not feel.
Since the magnitude 4.0 event, two smaller quakes—located deeper in Earth’s crust than the larger one—have already occurred: first a magnitude 2.7 tremor just to the northeast, then a magnitude 3.6 quake to the southwest of both these events.
Whether or not you felt the recent earthquakes, if you were in the area, you can report your experience to USGS to better inform its analysis of the event.