At noon, a M=3.0 earthquake struck just north of Berkeley, California, and caused shaking in both Oakland and San Francisco. According to the USGS, the quake occurred at a depth of 5 km, and was pure right-lateral strike-slip in nature. Based on the quake’s location, it likely occurred on the Hayward Fault, which extends from San Jose through the East Bay, across San Pablo Bay and through Santa Rosa (See figure below). However, the location of this quake is an outlier, as in the last decade, microearthquakes tend to occur to the east of the Hayward Fault, while this one took place to the west. Less than an hour after the earthquake, over 2,500 people had reported feeling the quake on the USGS website. However, based on where felt reports are coming in from, well over a million people will have felt the earthquake.
Based on the magnitude of this quake, it will not have caused any damage. However, it will have made lunchtime a bit more eventful for Bay Area residents and workers. The USGS forecasts that the Hayward Fault has a 33% chance of rupturing in a M=6.7+ earthquake by 2043. This is the highest probability of any fault in the Bay Area. The Hayward Fault last ruptured on October 21, 1868 in a M=6.8 event that killed 5 people and injured 30 others. Therefore, it is closely monitored and studied, and any earthquake on it, regardless of size deserves attention since a repeat event would be devastating to the East Bay. Should there be small aftershocks or other quakes along the Hayward Fault, we will be sure to update this post.
Berkeley Seismology Lab
R.W. Simpson, R.W. Graymer, R.C. Jachens, D.A. Ponce, C.M. Wentworth (2004), Cross-Sections and Maps Showing Double-Difference Relocated Earthquakes from 1984-2000 along the Hayward and Calaveras Faults, California, U.S. Geol. Survey Open-File Report 2004-1083.