By David Jacobson, Temblor
At 10:32 a.m. local time, a small M=3.3 earthquake struck just north of the city of San Jose, California. From USGS Felt Reports, of which there are over 800, we know that shaking was widely felt throughout the South Bay, with most people saying that shaking was “light.” Because of this quake’s small magnitude, no damage is expected.
This earthquake occurred at a shallow depth, and was pure right-lateral strike-slip in nature. Based on it’s location, slip was on the Hayward Fault, which extends from San Jose through the East Bay, across San Pablo Bay and through Santa Rosa. The Hayward Fault is of great importance because The USGS forecasts that it 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. Lastly, as can be seen in the Temblor map above, the San Jose area has an extremely high seismic hazard. This is because it is near the convergence of three major faults, the Hayward, San Andreas, and Calaveras fault.