Bay Area Earthquake Was Near Fault That’s Overdue for Intense Quake

A 4.3 magnitude earthquake jolted many in the Bay Area awake early Monday morning.

The shaking originated in Berkeley, where the United States Geological Survey originally reported a magnitude 4.6 earthquake at 2:56 a.m. just south of UC Berkeley’s campus. It was quickly downgraded.

The shaking appears to have caused no major damage or injuries, though many people took to social media saying it was the strongest shaking they had felt at their homes in the East Bay. For some, it stirred fears that the Big One could be close behind.

Scientifically, there isn’t much evidence that that’s true, but UC Berkeley earth science professor Roland Bürgmann said smaller quakes do raise the risk of another, including a large one, in the short term.

The USGS’s aftershock predictor indicates that there’s about an 18% chance of another quake greater than magnitude 3 in the surrounding region in the next week. The chances of a more significant event drop off quickly, though there’s about a 2% probability of an aftershock greater than magnitude 4.0 in the same time period.

Bürgmann said Monday’s quake was also interesting because its origin point was close to the Hayward Fault, which is about due for an intense quake. There’s about a 1 in 3 chance of a magnitude 6.7 or larger earthquake there in the next three decades, according to an earthquake outlook published by USGS in 2019.

Geological studies have found that the slip-strike fault generally has a large quake on an interval of 140 years, plus or minus 50. Its last major shake was in 1868, when a magnitude 7.0 caused more than $300,000 in damage and multiple deaths. Bürgmann said scientists believe it originated on the northern stretch of the fault closest to Monday’s quake, and the origin point of another magnitude 4.0 quake in 2018.

“Both the 2018 and the event today are right next to the part of the Hayward Fault that we believe is the part that produced the 1868 earthquake and could rupture again,” Bürgmann said.

KQED’s Ayah Ali-Ahmad contributed to this report.