A sequence of four earthquakes struck California's Bay Area on August 13, with the largest registering a magnitude 3.8. The tremors occurred along the Hayward Fault, a geological feature described by experts as "America's most dangerous" seismic zone.
The initial earthquake, measured at magnitude 3.8 by the U.S. Geological Survey (USGS), occurred at 11:30 a.m. ET (8:30 a.m. local time), approximately 14 miles from San Francisco. This was followed by three smaller aftershocks, with magnitudes of 3.0, 2.8, and 1.7, between 12:07 p.m. and 12:38 p.m. ET.
The shaking was felt by thousands across the Bay Area, with reports extending as far as Sacramento, about 75 miles east of San Francisco. The region is home to nearly eight million people.
The Hayward Fault, a 74-mile-long fault line that is part of the larger San Andreas fault system, is known for its potential to generate significant seismic activity. Scientists have warned that the fault is capable of producing earthquakes stronger than magnitude 7.0 and is considered overdue for a major event.
While Thursday's earthquakes caused relatively light shaking, they did lead to temporary disruptions in Bay Area Rapid Transit (BART) service. The train system experienced delays of up to 20 minutes after services were halted during the events. No injuries have been reported.
Scientists from California's Lawrence Livermore National Laboratory noted that the fault typically ruptures every 95 to 183 years. The last significant earthquake on the Hayward Fault occurred 158 years ago, in 1868. They have stated that the fault is overdue for an earthquake that could cause extensive damage to the densely populated area.
USGS scientists have previously issued warnings, indicating a 95 percent probability of an earthquake exceeding magnitude 6.7 striking near the Bay Area by 2043.