Researchers find no tsunami evidence, just one big Whidbey earthquake

Researchers search for tsunami evidence in two Whidbey Island locations have come up empty.

Researchers search for tsunami evidence in two Whidbey Island locations have come up empty.

However, the study did unveil a substantial shift in the ground level in the Crescent Harbor area, according to Jim Rich, volunteer with Island County’s department of emergency management and a retired oceanographer.

“We were looking for evidence of tsunamis,” Rich said. “We didn’t find one. More disturbingly, we found evidence of earthquakes.”

Instead of finding that Crescent Harbor was the recipient of tsunami waters triggered by a nearby earthquake, researchers determined that the area may have been the point of origin for an earthquake.

The shift could have been as deep as three meters, Rich said.

“The whole area sunk substantially,” he said. “That would have generated an earthquake.”

The study, which concluded July 17, was conducted in Dugualla Bay and Crescent Harbor in a partnership between the county’s department of emergency management and the Central Whidbey Lions Club.

Researchers from Central Washington University joined with local volunteers to piece together Island County’s history of tsunamis, earthquakes and other geological events. The study’s aim is to educate the island emergency management agencies on what to expect and how to be prepared.

Given the knowledge of the seismic activity in the Crescent Harbor area, the next question is whether the event is related to the known 1-meter shift at Rocky Point. And, further, if the two events were triggered by a larger Cascadia Subduction Zone event.

Both events lay on the Utsalady Point fault.

Rich said that if they are not related it’s bad news because it means the relationship between the faults has changed and they may trigger independently, which is tougher to plan for.

Results of the Crescent Harbor study revealed that changes in the rock content “can be explained by land level changes from earthquakes on the Utsalady Point fault, breaching or healing the beach berm, or a combination of the two,” according to CSU researcher Brian Ostrom.

Radiocarbon dating of samples will help researchers refine the date of the ruptures, Ostrom said.

Rich said three samples were submitted to an accelerator mass spectrometry lab in Bothel for carbon dating, and the results are expected any day.

If carbon dating confirms that the Rocky Point and Crescent Harbor events are connected, Rich said he expects the topic to gain interest at the Geological Society of America’s annual conference in Vancouver, B.C., in October.

“There’s a great expectation that we will get very good feedback from the world’s experts,” Rich said.

Moving forward, Rich said researchers plan to examine samples in Elger Bay on South Camano Island. The project, slated for sometime next year, aims to find out how the North Whidbey earthquake may have affected Coupeville, South Whidbey and Camano Island.

What researchers know for sure is that such an earthquake would not be good for Oak Harbor and that the majority of the damage would destroy Ault Field, a fact the Navy is painfully aware of, Rich said.

“The damage that would occur at Ault Field is not going to be repairable immediately,” Rich said. “They know there is very little prospect those runways will survive.”

 

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