Study says Northwest’s worst tsunami risk is underestimated


SEATTLE — It’s hard to imagine anything worse than the 2011 tsunami in Japan.

But a University of Southern California professor said an even larger tsunami could potentially hit the northwest coast if a mega-Cascadia earthquake strikes in an offshore corner.

“If these earthquakes occur entirely in the area, it should be very alarming,” Sylvain Barbot told KIRO 7.

The inner and outer slips are well offshore, between the beach and the underwater trench, and this is where the tsunamis are generated.

Barbot and his colleagues looked at earthquake data from around the world and found that even small earthquakes in the bevel can trigger large tsunamis.

Barbot also says that the width of the wedge matters.

“The wider that spot, the bigger the tsunami,” he said.

One of the widest points is off the northwest coast, around the Oregon-Washington border.

Barbot’s study found projections of a 65-foot worst-case tsunami in parts of Oregon are underestimated.

“We would actually put it at twice as much,” he said.

Barbot said there are many variables that can affect the height of a tsunami.

Harold Tobin of the University of Washington’s Pacific Northwest Seismic Network is cautious about the idea of ​​a giant tsunami.

“I think that’s an extreme case that’s really not very likely at all,” Tobin said.

Tobin said the USC study looked at tsunami hazard on a global scale and more localized work was needed to understand the dynamics off the northwest coast.

“I would take the Pacific Northwest numbers in there a bit with a grain of salt,” Tobin said.

There is active research to map the offshore wedge and how it would move during an earthquake.

In the northwest, tsunami risk is highest on ocean beaches, but it is possible for much smaller tsunamis to make their way to Puget Sound.

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