5.6 Earthquake Strikes Mendocino County, Triggers ShakeAlert Notifications Across Northern California

A magnitude 5.6 earthquake struck Mendocino County on Wednesday morning at 8:10 a.m., centered about seven miles north of Redwood Valley, and the quake triggered ShakeAlert notifications across Northern California.

The Sacramento Bee reported that Sacramento residents received an emergency earthquake alert even though they felt little or no shaking, with seismologist Dr. Angie Lux saying, "It only uses a couple of seconds of data to estimate the magnitude and the location of the earthquake."

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The San Francisco Chronicle said the U.S. Geological Survey identified the quake as the potential main shock of an earthquake sequence that included 44 seismic events, with a 77% chance of at least one magnitude 3 or greater aftershock in the area over the next week.

The Sacramento Bee also said the quake was near the Maacama Fault and that residents in Reno and Truckee reported receiving alerts Wednesday morning, with Lux saying communities as far away as Reno, Nevada and Medford, Oregon were within the alert’s range for light shaking.

The San Francisco Chronicle added that USGS said approximately 80,000 people experienced moderate to very strong shaking, while about 10 million people felt weak to light shaking.

The San Francisco Chronicle reported that the quake sent smartphone alerts to around 657,000 people across much of Northern California, including the Bay Area, and it said hospitals had reported some injuries while details were not immediately available.

Mendocino County spokesperson Heather Rose said, "Hospitals had reported some injuries, though details about their number or severity were not immediately available," as the Chronicle also reported county officials said there were no immediate reports of major damage.

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The Sacramento Bee described how earthquake alerts were sent through MyShake, Android’s earthquake alert system and other participating platforms after three computer algorithms analyzed the quake’s first seismic signals.

The Sacramento Bee quoted Dr. Angie Lux explaining the system’s purpose, saying it is designed to alert "as many people who may feel shaking as possible," and it said Sacramento sat on the fringe of the area expected to experience light tremors.

The San Francisco Chronicle reported that PG&E’s outage center showed more than 7,400 PG&E customers across Mendocino County were without power after the quake, with Willits among the hardest-hit areas.

The Sacramento Bee said Lux encouraged residents to check the U.S. Geological Survey’s website for forecasts of additional aftershocks, which are common after a magnitude 5.6 earthquake.

“Along California's northern coast, where three massive tectonic plates meet, intense but invisible seismic activity has just revealed its secrets”

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Lux told the Sacramento Bee there is a "very, very, very small chance" Wednesday’s earthquake was a foreshock to a larger event, and she said seismologists won’t know whether that’s the case until later.

The San Francisco Chronicle reported that a spate of small aftershocks followed, with all aftershocks less than magnitude 3.0, and it said the quake hit at 8:10 a.m. about 7 miles north of Redwood Valley, east of Willits, at a depth of about 5 miles.

The Sacramento Bee quoted Lux saying, "We live here in California, so we definitely anticipate earthquakes," and it urged residents to use the quake as a reminder to be prepared for the next big earthquake.

The San Francisco Chronicle also said the governor’s office stated, "The Governor’s Office is closely coordinating with emergency officials and assessing potential impacts and damage," as emergency crews checked for damage across the region.