A powerful 7.0 magnitude earthquake struck off the California coast Thursday morning, rattling homes and prompting a brief Tsunami warning that left residents and boat operators scrambling to prepare. Despite the initial concerns, the event caused minimal damage.
The earthquake occurred at 10:44 a.m., about 60 miles west of Petrolia in Humboldt County, a region known for its seismic activity due to the Mendocino Triple Junction where three tectonic plates converge. The warning predicted a potential tsunami arrival in Noyo Harbor at 11:10 a.m., leaving boat owners and operators little time to act.
“We just hung out here in the harbor and kept an eye on things,” said Nick Kidd, a commercial fisherman. “We didn’t want to get caught in between, so we decided to stay put.”
Emergency alert systems activated swiftly. “The warning sirens went off in both the north and south harbors, which is great because we don’t use them often,” Anna Neumann, the harbor master, said. “Most people receive alerts on their cell phones, so it’s all very obvious what is occurring.”
The U.S. Coast Guard moved two vessels offshore to support boats that chose to leave the harbor, as vessels are safer offshore. Neumann described a very minor surge resulting from the quake, with water levels rising and falling by about four to six inches over several minutes.
The Tsunami warning was cancelled at 11:55 a.m.
Meanwhile, the quake was followed by more than a dozen smaller aftershocks.
The earthquake’s geology played a key role in the limited impact. Stephen DeLong, a supervisory research geologist with the U.S. Geological Survey, noted that most of the quake's motion was horizontal rather than vertical, minimizing the likelihood of a tsunami.
“This area, the Mendocino Triple Junction, is where the Cascadia subduction zone, Mendocino Fault, and San Andreas Fault meet,” DeLong said.
“In this case, we think of this as a right lateral earthquake," DeLong added. "So most likely the plate to the north of this earthquake moved to the right and the plate to the south moved to the left. And because of this strong motion, there was initially concern about tsunamis, but it's very likely that most of the motion was actually horizontal rather than vertical, which is what tends to cause tsunamis caused by earthquakes."
For local authorities, the event functioned as a valuable emergency drill. Mendocino County’s Emergency Services Coordinator Jeff Adair said no significant damage was reported.
Adair urged residents to prepare for the next quake by downloading the MyShake app for earthquake alerts.
“We got about a minute’s warning before the shaking hit here in Ukiah,” Adair said.
For people who find themselves in a Tsunami inundation zone during a powerful earthquake, every minute counts. They should seek higher ground as soon as possible, and not wait for emergency alerts, Adair said.
Governor Gavin Newsom proclaimed a state of emergency in Del Norte, Humboldt, and Mendocino Counties, saying: “Today’s emergency proclamation will allow more resources to go where needed for emergency response to this morning’s earthquake. I am grateful for the robust system our state has in place that worked as intended today and kept people safe and informed."