[Update from Mendo OES] Geology Expert: Mendocino Quake No Surprise; Aftershocks Expected

Cropped photo of damage in Willits residence. Photo submitted.

The ground has settled — for now — but Mendocino County is still picking up the pieces this morning after a magnitude 5.6 earthquake struck north of Redwood Valley at 8:10 a.m., and the region’s leading earthquake scientist says residents should expect more shaking before the day is out.

Lori Dengler, Emeritus Professor of Geology at Cal Poly Humboldt, said three aftershocks of magnitude 2.5 or greater had already been recorded by mid-morning. The USGS aftershock forecast puts the probability of a magnitude 3 aftershock at 90 percent, with a smaller chance of a magnitude 4.

Map showing the Maacama fault zone (to the left) in Mendocino County. Credit: U.S. Geological Survey

“Whenever there’s an earthquake, there’s always a teeny tiny chance that this earthquake will be followed by an earthquake of equal size or perhaps larger,” Dengler said. “Teeny tiny — but it’s there.”

The quake struck on the Maacama fault, a strand of the broader San Andreas system that Dengler said is capable of producing earthquakes in the magnitude 6 to 6.5 range. More than 38,000 reports had been submitted to the USGS Did You Feel It page by mid-morning, with felt reports stretching from south of San Jose to the Medford area of Southern Oregon.

Dengler, who was on a dog walk near the Arcata airport when the quake hit, said she didn’t feel it herself — but her phone lit up immediately with a MyShake alert reading magnitude 6, Mendocino County. A revised figure of 5.6 came in minutes later.

Wednesday’s quake posed no tsunami threat, she said, given its size and distance from the coast. But she used the moment to remind coastal residents of a standing rule.

“When you feel the earthquake, that should always be your sign to go inland, to get off the beach,” Dengler said. “That could well be our greatest threat in the next large earthquake.”

Screenshot of USGS map showing 5.6M quake and aftershocks.

On the ground

Power restoration in the hardest-hit areas was still hours away as of mid-morning. Laytonville’s estimated restoration time was 3:15 p.m. Crews were working multiple zones across Willits simultaneously.

Both the Laytonville clinic and the Round Valley clinic were operating on backup generators, Mendocino County Sheriff Matt Kendall confirmed. CHP checked all bridges and overcrossings in the Laytonville area and reported no structural damage.

Kendall said scattered power outages had affected the Cahto Tribe in Laytonville, and items had fallen off walls in homes across the area. The county’s OES cooperators are holding a damage assessment meeting this morning to begin coordinating the broader response.

No injuries had been confirmed as of mid-morning.

Screenshot of PG&E Outage Map

Preparedness reminder

Dengler said Wednesday’s quake is a useful reminder that the North Coast lives with seismic risk every day.

“We’re one day closer to the next damaging earthquake than we were yesterday,” she said. “You’re going to survive that next big earthquake — but you’re going to be really uncomfortable if you have not taken action to store food and water beforehand. Think being stuck without anything for two weeks.”

The Redwood Coast Tsunami Work Group posts real-time earthquake and tsunami updates on Facebook at RCTWG and maintains a preparedness website at rctwg.humboldt.edu. Mendocino County residents can monitor mendoready.org for official updates.

Felt reports can be submitted to the USGS at earthquake.usgs.gov.

Redheaded Blackbelt will continue updating this story as conditions change. Readers with damage reports are encouraged to share them in the comments.

Update from the Mendocino Office of Emergency Services:

The County of Mendocino Emergency Operations Center is open and in monitoring status. At this time, there are no known major damages, but we are working with our operational area partners to continue to assess damages.

Some injuries have been reported, but no deaths.

PG&E has reported power outages with over 6000 residents without power, in Willits, Laytonville, Leggett, Round Valley/Covelo.

In the interim, the County encourages residents to stay off major roadways to allow for Caltrans, PG&E and County workers to perform damage inspection and repairs.

For more information, or to report damages in your area, visit MendoReady.org.

Earlier: [Update: 7400 Without Power] 5.6 Earthquake Rattles Mendocino County; Power Lines Down in Willits, CalFire Assessing Damage5.6 Earthquake Strikes Mendocino County