A magnitude 3.3 earthquake rattled the Santa Rosa area Thursday morning, Sept. 3, the shaking felt as far away as the East Bay and leading to local school evacuations, though no damages were reported.
The U.S. Geological Survey initially estimated the temblor’s size at 3.5 before revising its measurement early Thursday afternoon.
The earthquake struck shortly after 10:30 a.m. about 2 miles east-southeast of the unincorporated Larkfield-Wikiup area north of Santa Rosa, according to the USGS. It originated about 4.6 miles below surface.
The strongest shaking was reported in parts of Santa Rosa, including the Fountaingrove and Coddingtown areas. Shaking was also reported as far away as Hayward, according to reports submitted to the USGS.
Sonoma County emergency officials received no reports of damage from the earthquake as of Thursday afternoon, said Karen Hancock, a spokesperson for the Sonoma County Department of Emergency Management. Paul Lowenthal, division chief fire marshal for the Santa Rosa Fire Department, said the agency had not received any calls for service related to the quake.
Santa Rosa City Schools notified families Thursday that initial inspections found its school facilities safe and that all campuses would continue operating normally.
Santa Rosa High School evacuated as a precaution, but no early dismissals were planned, district spokesperson Patrick Gannon said. The Mark West School District, which serves the area near Larkfield-Wikiup, also said it did not plan any early dismissals.
“This was good, real-life practice,” Gannon said. Earthquakes, he added, are “a reality in California that we have to be ready for.”
The district, which plans to participate in The Great California ShakeOut, a statewide earthquake drill on Oct. 15, said it would continue checking its buildings and monitoring for possible aftershocks Thursday.
The earthquake occurred near the Rodgers Creek Fault, which runs through central Sonoma County. The fault is part of the Hayward-Rodgers Creek fault system, which extends through the North Bay and East Bay and is capable of producing major earthquakes.
Two earthquakes with magnitudes of 5.6 and 5.7 struck near Santa Rosa along the Rodgers Creek Fault in October 1969, causing significant damages to homes and businesses in the area. More recently, a pair of 4.4 and 4.3 magnitude temblors on the fault in September 2022 jolted the Larkfield area and damaged several homes.
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The Press Democrat, 2022
Rodgers Creek Fault (The Press Democrat, 2022)
Multiple Santa Rosa City Schools elementary campuses sit on or near parts of the Rogers Creek Fault. One of the campuses, Brook Hill Elementary School, closed last year, and the Santa Rosa French-American Charter School was vacated in June, relocating to the former Santa Rosa Middle School Campus. Gannon said the district studied the fault line last year to inform planning for updates to existing facilities and future construction projects.
“The more we learn about fault lines, that helps us,” Gannon said. “Over time, in our Facility Master Plan, we have a shift to where the buildings on campus will be located. Any modern buildings will be built away from that line.”
With the most intense shaking felt Thursday in the Santa Rosa area, some residents questioned on social media why they did not receive an emergency alert on their phones when the earthquake struck. Hancock said Sonoma County’s SoCoAlert system does not automatically issue earthquake warnings. Earthquake early warnings are handled through the U.S. Geological Survey’s ShakeAlert system and UC Berkeley’s MyShake app.
Thursday’s earthquake was below the level that would typically trigger either system, Hancock said. USGS wireless emergency alerts — the loud notifications similar to Amber Alerts — generally target earthquakes of magnitude 5 or greater, while MyShake notifications can be issued for earthquakes of magnitude 4.5 or greater.
Hancock said Thursday’s earthquake also served as a timely reminder that September is National Preparedness Month. She encouraged residents to review their emergency plans rather than wait for a larger disaster.
When the earthquake struck, Hancock was meeting with community organizations that work with the county during emergencies. Those in the room immediately dropped, covered and held on — the recommended response during an earthquake.
“It’s a little jump-start for National Preparedness Month,” Hancock said.
Residents should know where they can safely take cover during an earthquake, review emergency plans with family members and at work, and remain alert after shaking stops, she said. Even after a relatively small earthquake, additional shaking can follow.
“Sometimes this gets away from us, or may never come up,” Hancock said of emergency planning. “So we have to have these little events or little reminders to kind of jump-start some of us.”
You can reach Staff Writer Isabel Beer at [email protected] and Staff Writer Hannah Harn at [email protected].
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