A magnitude 4.6 earthquake centered in Santa Cruz County rattled Northern California early Thursday morning, waking people up as far away as San Francisco.
The earthquake hit at 1:41 a.m. The epicenter was less than a mile away from the Santa Cruz County community of Boulder Creek. It was about 11 miles northwest of Santa Cruz, 19 miles southwest of downtown San José, and 48 miles southeast of downtown San Francisco.
The quake occurred near the San Andreas fault, according to Jessica Sigala, a geophysicist with the U.S. Geological Survey.
“For the area, it’s normally not this large,” she said. “We can expect aftershocks less in magnitude for the next hour to several days.”
The earthquake was originally reported as a 4.9 magnitude quake through the earthquake early warning system, but because the warning was sent out with very little data to work with, it wasn’t the most accurate initially, according to Sigala.
“The notification is sent out in order to warn people and it goes out within minutes of the earthquake occurring, but as we get more data from around the world, our magnitude can become more stable,” she said.
After a few minutes, the 4.9 magnitude earthquake was downgraded to a 4.6.
There were no reports of immediate damage, according to the California Department of Forestry and Fire Protection’s San Mateo-Santa Cruz Unit.
Moderate shaking, as defined by the Modified Mercalli Intensity Scale, was felt in the Santa Cruz Mountains closest to the epicenter, according to the U.S. Geological Survey. In general, moderate shaking is enough to wake people up, and is capable of breaking dishes and windows.
A magnitude 4.6 earthquake struck 11 miles northwest of Santa Cruz.
(U.S. Geological Survey)
Light shaking was felt across Silicon Valley, and weak shaking across the rest of the San Francisco Bay Area, according to the USGS.
The earthquake occurred close to the Zayante fault, which runs parallel to the San Andreas fault. The Zayante and San Andreas faults are considered to be faults that pose the most serious shaking threats in the Santa Cruz County area, according to county officials.
A number of people across Northern California reported hearing the alerts generated by the USGS ShakeAlert earthquake early warning system before feeling the shaking.
Thursday’s earthquake epicenter was about 14 miles northwest of the starting point of the magnitude 6.9 Loma Prieta earthquake of 1989, which caused the collapse of a section of Interstate 880 in Oakland and a partial collapse of a section of the San Francisco-Oakland Bay Bridge. The 1989 earthquake caused at least 63 deaths, and was the largest earthquake on the San Andreas fault since the great 1906 San Francisco earthquake.
This story originally appeared on LA Times
