Earthquake News

318 years ago a M9 'megathrust' quake hit the northwest

The northwest is reminded on Friday of how the Cascadia Subduction Zone – a fault that sits along the bottom of the Pacific Ocean stretching from Northern Vancouver Island to Northern California – could cause the worst natural disaster in the history of North America.

It was 318 years ago it produced a magnitude 9 megathrust earthquake. Washington State Department of Resources wrote a blog post on Friday about the event.

On Jan. 26, 1700, the Cascadia subduction zone produced a Magnitude 9 megathrust earthquake that ripped a 1,000-kilometer tear just off the North American coast, shaking and flooding land from British Columbia to California.

Oral traditions from the Quileute and Hoh tribes described the night the Thunderbird and Whale fought, shaking mountains, uprooting trees and covering the land with ocean water.

Geologists say the event was the result of the Juan de Fuca tectonic plate pushing under the larger North American plate. The violent subduction resulted in the quake that dropped the coast as much as 6 feet and produced a tsunami that reached almost 1,000 feet inland.

But it was the Cascadia quake’s impacts some 4,700 miles across the Pacific Ocean that allowed scientists to properly date and time the geologic event to around 9 p.m. Jan. 26, 1700.

Records in Japan told of the Orphan Tsunami of 1700. That documented tsunami, combined with analysis of red cedar trunks by scientists like Brian Atwater of the United States Geologic Survey revealed land subsidence and seawater inundation that submerged coastal forests.

This day in history has many asking, what about the next one?

The Cascadia Subduction Zone usually ruptures every 200 to 500 years. It’s impossible to predict when a monster quake occurs. But tectonic stresses have been accumulating in the CSZ for more than 300 years.

Pacific Northwest Seismic Network reports that the fault has the ability to produce another M9 quake if it ruptures entirely.

Emergency management leaders encourage families to have a plan in the event of a disaster. People should prepare to survive on their own for seven to 10 days.

In the meantime, state leaders and geologists have practiced emergency drills and created scenarios to better understand how a seismic event may unfold.

But Washington DNR writes that there’s more work to be done. Washington does not have an inventory of the seismic hazard for critical infrastructure, and the state is working off outdated tsunami inundation maps, according to DNR.

DNR is pushing for a funding packing that would allow production for better maps and systems that would keep communities safe.


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