A magnitude 3.8 earthquake occurred Thursday morning near the Oakland Zoo, rattling communities across the San Francisco Bay Area and serving as a reminder of the seismic threat posed by the Hayward Fault. The quake, initially reported as magnitude 4.1 before being downgraded, was followed by two aftershocks measuring 3.0 and 2.8.
The epicenter was located near the Oakland Zoo, which sits directly on the Hayward Fault. This 74-mile seismic fault runs through heavily populated areas, including Berkeley, Oakland, and Fremont. Scientists have long expressed concern about the fault's potential to produce a major earthquake.
The Hayward Fault is considered one of the most dangerous in the United States and is capable of generating earthquakes exceeding magnitude 7. It last experienced a significant rupture in 1868. Experts warn that the fault is overdue for another major earthquake, with scientists estimating that major quakes occur along the fault every 95 to 183 years.
The U.S. Geological Survey (USGS) estimates a 14.3% probability of the fault producing a magnitude 6.7 or greater earthquake by 2034, and a 33% chance by 2043. USGS earthquake geologist emeritus David Schwartz has described the fault as a "tectonic time bomb."
Researchers from Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory have conducted simulations of a magnitude 7 rupture. Their findings suggest that shaking in some Bay Area communities could be up to 50% stronger than previous forecasts. Areas identified as vulnerable to particularly powerful ground motion include Oakland, Berkeley, Hayward, San Leandro, Emeryville, Alameda, and Livermore.
A USGS disaster scenario projects that a major earthquake on the Hayward Fault could result in 800 fatalities and up to 18,000 injuries. The potential destruction includes widespread fires, the destruction of tens of thousands of homes, and the displacement of nearly half a million people.
No major damage or injuries were immediately reported from Thursday's earthquake. Thousands of people reported feeling the tremor, with shaking felt as far north as Santa Rosa and Sacramento, and as far south as Santa Cruz.