Quake raised brief local tsunami concerns

Published 5:00 pm Thursday, December 5, 2024

PACIFIC COUNTY — One of the biggest earthquakes to strike off the Pacific Coast of the continental United States in recent memory led to brief concerns that the southern Washington and northern Oregon coasts could be at risk of a tsunami.

A magnitude 7.0 earthquake struck about 45 miles off the coast of northern California near Eureka in the early afternoon of Dec. 5, leading the U.S. National Tsunami Warning Center (NTWC) to initially issue a tsunami warning as far north as the mid-Oregon coast while danger levels for other U.S. and Canadian Pacific coastal areas were continuing to be evaluated.

The threat of a tsunami for all U.S. and Canadian Pacific coastland was ruled out about an hour later, and no tsunami waves were ultimately observed in the aftermath of the large quake.

In a review of the day’s events, Scott McDougall, Pacific County Emergency Management Agency’s director, said his agency was notified by NTWC about the earthquake and uncertain tsunami danger at 11 a.m., while he and emergency management coordinator Marcelina Medina were in Ocean Shores to pick up shelter supplies.

“As soon as the information was received PCEMA began notifying our stakeholders and the public,” he said, which included the Pacific County Dispatch Center, the City of Long Beach, Pacific County General Administration, county commissioners and Sheriff Daniel Garcia.

“We also began making social media posts. Our message was very simple. A Tsunami Warning, Watch, or Advisory was never issued for the northern Oregon or Washington coastlines. The Tsunami Warnings for the northern California and the southern Oregon coast were only issued due to their immediate proximity to the earthquake.”

The quake was a strike-slip earthquake that occurred along the Mendocino Escarpment, and no considerable tsunami was generated near the earthquake’s epicenter. Strike-slip earthquakes, according to the U.S. Geological Survey, are less likely to cause a tsunami because the “movement is primarily horizontal with minimal vertical movement of the ocean floor.”

McDougall stressed the need to stay calm in situations like these, citing reports of people driving up into the hills to escape the path of the tsunami. While applauding their resolve and preparedness, he said it was important to have the facts “and understand that a mass evacuation would likely be more dangerous than most distant source tsunamis we will face here.”

“If a warning is issued and evacuations are needed, we will provide detailed instructions about who will be impacted, thereby taking an element of danger out of the equation,” he added.

A 7.0 earthquake is classified as “major” and could have caused serious damage if it occurred onshore. California experiences a quake of this magnitude about every 20 years on average.