Northern California Earthquake: Initial Reports

A magnitude 4.9 earthquake rattled Northern California early Thursday morning, waking residents across the Bay Area. The quake struck at 1:41 a.m., with the epicenter located near Boulder Creek in Santa Cruz County.

Earthquake Location and Intensity

The epicenter was less than a mile from Boulder Creek, approximately 11 miles northwest of Santa Cruz, 19 miles southwest of San Jose, and 48 miles southeast of San Francisco. According to the U.S. Geological Survey (USGS), moderate shaking was felt in the Santa Cruz Mountains closest to the epicenter.

Shaking Levels Across the Region

Moderate shaking, as defined by the Modified Mercalli Intensity Scale, is strong enough to wake people and can cause dishes and windows to break. Light shaking was reported across Silicon Valley, while weak shaking was felt throughout the rest of the San Francisco Bay Area.

Fault Line Activity and Early Warnings

The earthquake occurred near the Zayante fault, which runs parallel to the San Andreas fault. County officials consider both the Zayante and San Andreas faults to be significant shaking threats in the Santa Cruz County area. Many residents reported receiving alerts from the USGS ShakeAlert earthquake early warning system before experiencing the shaking.

Historical Context: Loma Prieta Earthquake

Thursday’s earthquake epicenter was approximately 14 miles northwest of the starting point of the magnitude 6.9 Loma Prieta earthquake in 1989. The 1989 Loma Prieta earthquake caused widespread damage, including the collapse of a section of Interstate 880 in Oakland and a partial collapse of the San Francisco-Oakland Bay Bridge.

Impact of the 1989 Earthquake

The 1989 Loma Prieta earthquake resulted in at least 63 deaths and was the largest earthquake to hit the San Andreas fault since the devastating 1906 San Francisco earthquake. As of now, the California Department of Forestry and Fire Protection’s San Mateo-Santa Cruz Unit has reported no immediate damage from Thursday’s event.