Map courtesy of the U.S. Geological Survey
Lori Dengler said she wasn’t surprised that Thursday’s magnitude 7.0 earthquake only produced a tsunami that topped out at roughly 8 inches in Crescent City.
But, while Dengler, geology professor emeritus at Cal Poly Humboldt, is still going through the reports and is speaking with the media about today’s temblor, she said one of the outcomes might be a rethinking of how the U.S. approaches tsunami evacuations.
“The Tsunami National Warning Center in Palmer, Alaska has developed a template for if an earthquake happens here and it’s in this magnitude range, this is what we do,” Dengler, whose expertise is in geophysics, earthquake and tsunami hazards and hazard reduction, told Redwood Voice Community News on Thursday. “Because this earthquake was so relatively close to the coast and their preliminary magnitude was 7.3, it immediately triggered a tsunami warning from basically Santa Cruz to Central Oregon.”
This includes the San Francisco Bay Area, though most seismologists knew that the tsunami the quake would produce wouldn’t be large enough to get through the narrow mouth, Dengler said. Still, “we all must err on the margin of safety,” she noted.
“The only area where we would expect significant surges would have been along the Humboldt and Del Norte County Coast,” Dengler said. “And one is always worried about Crescent City. It doesn’t take much to excite waves there.”
Though it took a bit to narrow down the epicenter and magnitude, seismologists with the U.S. Geological Survey say the earthquake struck about 39 miles west of Petrolia on the Mendocino Fault at about 10:44 a.m. Thursday.
Though primarily felt between Monterey and Coos Bay and as far east as Carson City, Nev., according to Dengler, one person from Vancouver said they felt shaking as did two people in Seattle. The quake was also felt as far south as Los Angeles, Dengler said.
Though these earthquakes were off the coast, they had nothing to do with the Cascadia Subduction Zone, Dengler said. The Cascadia Subduction Zone stretches from Northern California to Vancouver Island and can produce earthquakes of 9.0 or greater and tsunamis reaching 30 meters in height.
“The Mendocino fault is this major fault somewhat similar to the San Andreas fault in that the two sides typically move side by side relative to one another,” Dengler said. “We’ve had over 200 earthquakes of magnitude 4 or larger since 1990, so it’s a very active fault and every year we see earthquakes typically in the magnitude 5 range.”
Just before 3 p.m., Dengler said the reports she was seeing determined that Thursday’s earthquake was a strike-slip earthquake. She said she was expecting this determination noting that unless it produces a landslide, strike-slip earthquakes typically don’t produce major tsunamis.
“A 6-8 inch tsunami in Crescent City sounds right,” she said.
As of about 11 a.m., the Del Norte County Office of Emergency Services were advising people in the inundation zone to evacuate to an area north of 9th Street in Crescent City. Emergency Services Manager Deborah Otenberg told Redwood Voice Community News that surges were predicted to reach shore at about 11:20 a.m.
The National Tsunami Warning Center canceled the warning after about an hour. According to Interim Harbormaster Mike Rademaker, Commissioner Rick Shepherd reported watching a water surge that rose about 6 to 8 inches before dropping after about 4 to 5 minutes.
Otenberg said she used IPAWS, the Integrated Public Alert Warning System operated through FEMA, to reach more than 28,000 people, even those who weren’t registered to receive local alerts and those who didn’t live on the coast.
“We didn’t want to have people going down the coastline or driving through and putting themselves in danger,” she said.
Despite a Facebook post on a local scanner feed saying the tsunami warning and evacuation “caused mass panic in Crescent City,” Crescent City Police Chief Richard Griffin said there was one car wreck at Lauff and J streets, a hit and run, but he didn’t see widespread panic.
Traffic was backed up as people tried to get out of the inundation zone via car, but Griffin, who worked for the Del Norte County Sheriff’s Office when Tohoku earthquake in Japan sent a tsunami toward Crescent City in 2011, deemed Thursday’s evacuation “about average.”
“You had parents who were getting their kids, which they probably shouldn’t have. But we didn’t have any looting,” he said. “No matter how much you train, some people are going to ‘panic’ and try and go.”
Griffin said his officers evacuated about six people out of Beachfront Park before helping the residents at Surf Apartments get to higher ground. CCPD worked with the Del Norte County Sheriff’s Office, the California Highway Patrol, California State Parks and Del Norte County Probation.
Sheriff Garrett Scott echoed Griffin’s assessment that the evacuation went well. The alert he received said to be prepared for a near-shore emergency, which doesn’t give people enough time to gather their things and prepare for an evacuation, he said.
“We’ve had a number of those over the last 10, 15, 20 years and I’ve seen it so chaotic [where] there’s many car crashes and intersections where vehicles are just left because people get so frantic, so I think the community did really well and knew they just needed to evacuate,” he said.
In addition to the agencies Griffin listed, Scott said the Yurok Tribal Police department helped get Klamath residents to safety as did the National Park Service.
“We were able to really focus on the beaches and people surfing or walking on the sand — make sure to hit those low-lying areas that are really critical for evacuating as soon as possible,” Scott said. “There are some houses that sit really low to sea level and so those are pre-mapped out and our [deputies] were able to get those notifications made right away. It’s definitely scary for everybody and we’re thankful there was no wave action and no real damage that we’ve discovered in Del Norte.”
Though Del Norte fared well through the earthquake and tsunami, Dengler said people may want to take the time to find out if they live in a tsunami hazard zone. Del Norte County and Crescent City has brochures with evacuation maps while the Redwood Coast Tsunami Working Group has a website that includes an interactive map for the entire state, she said.
Dengler also pointed out that an earthquake that produces a “real tsunami” will likely shake for a lot longer than Thursday’s temblor did. In that case, people shouldn’t wait for an official evacuation alert, she said.
“That shaking that lasts a long time might be very modest shaking, but it goes on and on and on, that’s my signal to get out of the tsunami zone,” she said. “And I’ve got to do that on my own and preferably by foot because the roads could be damaged. I really worry that we will have more casualties due to a messy evacuation than due to any surges. It’s always best to go on foot.”
