PORTLAND, Ore. — A Thursday morning tsunami warning for parts of the southern Oregon and northern California coast has been lifted. The National Weather Service announced just before noon that no destructive tsunami had been recorded and there was "No Tsunami Warning, Advisory, Watch or Threat" anywhere along the coast.
NWS urged residents not to return to the hazard zones until cleared to do so by local emergency officials. Officials closed all state park beach access points along the Oregon Coast during the warning period, and the Oregon Department of Emergency Management (OEM) said early Thursday afternoon that the beaches would remain closed until 3 p.m.
The National Tsunami Warning Center in Alaska issued the warning minutes after a magnitude 7.0 earthquake struck off the coast, about 45 miles to the southwest of Eureka, California at 10:44 a.m. Thursday. The U.S. Tsunami Warning System initially reported an estimated magnitude of 7.3, which was revised to 7.0 a short time later.
The warning zone extended south from the Douglas and Lane county line about 10 miles southwest of Florence, all the way to Davenport, Calif., about 10 miles northwest of Santa Cruz. At least 5.3 million people in California were impacted by the warning.
While brief, the warning was a test and a reminder for coastal towns of a very real threat, like in Reedsport, a town on the Umpqua River only a few miles away from the Pacific Ocean.
The quake was felt hundreds of miles away, as far south as San Francisco, where residents felt a rolling motion for several seconds. It was followed by smaller aftershocks. U.S. Geological Survey officials encouraged residents to be ready for more aftershocks throughout the day.
More than 1.3 million people lived close enough to the quake that they could have felt it, the USGS estimated. There were no immediate reports of major damage or injury.
'We live in earthquake country'
Earthquakes on the scale of Thursday's event are relatively common in the southern Cascadia area, according to Professor Diego Melgar with University of Oregon Earth Sciences, and are a "fact of life" in Eureka and other nearby cities.
"We live in earthquake country in northern California and southern Oregon," he said. "These events are a fact of life, and when they happen, sometimes they can be accompanied by significant tsunamis, and that's why we have these protocols for warning and evacuation in place."
The earthquake originated from the Mendocino Fracture Zone where the Pacific and Juan de Fuca tectonic plates intersect, according to OEM, which is part of a larger intersection area of three plates off the coast of Oregon and California called the Mendocino Triple Junction.
The Pacific Northwest is famously due for a major earthquake that could strike at any time, but Melgar said it's hard to know if the coastal earthquake means anything in terms of when the "big one" might arrive.
"This event is comparably small, compared to what we expect from the really big one," he said. "Even though I know it felt really strong to folks and that there's a flurry of activity right now — it was still a significant event — but it doesn't necessarily mean that we're any closer to the next big event."
A megaquake has the potential to produce devastating tsunamis that could threaten coastlines around the entire Pacific Ocean. Thursday's earthquake ultimately didn't produce a tsunami, and Melgar said even if it had, a magnitude 7 seismic event would probably consist of strong currents and waves no bigger than a few feet.
"Still quite hazardous," he added, "so it's important for people to follow the directions of their emergency managers and weather offices and evacuate the beaches when necessary."
Cascadia Subduction Zone
In Portland, experts say "the big one" would be connected to a fault called the Cascadia Subduction Zone, which stretches from Vancouver B.C. down to northern California.
"It goes off every 700 years on the average, and that's a [magnitude] 9!" said Portland State University geology professor Scott Burns. "It's going to cause huge amounts of devastation in that whole area."
Burns said the last major earthquake connected to the Cascadia Subduction Zone hit the Portland region 400 years ago, putting us in the danger zone right now.
"People are like, 'Oh, we have 300 years to go,' but not really," said Burns. "That's based on averages, and when you look at the last 10,000 years of earthquakes, some of them are short periods, some of them are long periods — those are all averages."
As far as tsunami danger, Burns said it can happen on the Oregon coast for two other reasons besides a Cascadia Subduction Zone earthquake: seismic activity in Alaska topping magnitude 7 and seismic activity over magnitude 8 in Japan. He noted the earthquake that hit Japan in 2011, which generated a tsunami wave that hit parts of the Oregon Coast, even damaging a marina in Brookings. In 1964, an earthquake in Alaska caused 30-to-50-foot tsunami waves in Seaside and Cannon Beach.
Monitoring earthquakes in the Northwest
When it comes to monitoring earthquakes in the region, the Pacific Northwest Seismic Network has spent the last decade working to expand their array of seismometers.
Back in 2014, the United States Geological Survey (USGS) had 240 seismometers, and they set a goal of 600 seismometers needed to properly cover the Northwest. Now, there are now nearly 700.
“The shaking from that epicenter is going to hit a station sooner if there's more stations. If we only have a handful of stations, that seismic wave may have to travel dozens of miles before it's detected, which eliminates several seconds of potential extra warning,” explained Doug Gibbons, research engineer at the Pacific Northwest Seismic Network.
Three stations are needed to triangulate which direction the shaking is coming from, he said, and the closer they are to each other, the more accurate the reading.
But there's one problem with the seismic network that Thursday’s scare certainly highlights: All of those nearly 700 seismometers are on land.
Scientists are working to add underwater stations off of Oregon’s coast, but not until 2026. They'll be plugged in using underwater cables to further improve early warnings to communities along the coast.
Preparation is key
While evacuation notices were called off Thursday, state officials said the process helped them plan for the future.
"This was a great opportunity to look at how we respond to these no-notice events, like tsunamis and earthquakes," said Althea Rizzo, geologic hazards coordinator at the Oregon Department of Emergency Management.
Rizzo said following the California quake, state and local agencies did well in alerting people of evacuation notices.
"They responded exactly how they're supposed to respond, proactively and getting people to safety as quickly as possible," she said.
State safety officials want people to look at their new Be 2 Weeks Ready program. It's a tool kit designed to help prepare for survival after natural disasters from storing food and water to planning for waste, hygiene and shelter. In addition to having supplies ready for an earthquake or tsunami, Rizzo said now is the time to come up with an emergency plan for your family, including possible evacuation routes and a communication plan, and make sure you're signed up to get emergency alerts on your phone.
Professor Burns said he hopes everyone sees Thursday's quake as a wake-up call they should take seriously.
"The No. 1 thing is this is a reminder that we live in earthquake country and that everybody needs to be prepared," said Burns. "When 'The Big One' happens — and it's not if but when — we want everyone to be prepared; the more prepared we are, the less damage the quicker recovery is going to be."
The Associated Press contributed to this story.