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READY TO RUMBLE What Happened In Sumatra Could Happen To The West Coast

| posted on July 22, 2010


“Cascadia subduction zone tsunamis could conceivably cause the loss of tens of thousands of lives on the Pacific Northwest coast of North America. Paleoseismic and other data support Cascadia earthquakes with moment magnitudes of nine or higher, rupture lengths of more than 1000 km and a recurrence of 400-600 years; the last event was 301 years ago, so the conditional probability of another occurring in the next 100 years is high.”

From Priority directions for research on tsunami hard estimation: Cascadia Subduction Zone, Pacific Northwest coast of North America by George R. Priest, Oregon Department of Geology and Mineral Industries, Newport, Oregon

If any place along the Pacific Coast is likely to get worked, Crescent City is it.

After surviving a giant wave at Makaha during
the legendary Swell of 1969, Greg Noll pulled a Sisyphus, packed up
his family and walked away from surfing, looking for something else to do. He went to Crescent City, California, in far
Northern California, and people wondered what he was doing. Noll said
he was fishing, but maybe he was waiting for something even bigger
than what he had encountered at Makaha, because Crescent City has a
reputation for giant waves, and the Big One is lurking, just over the
horizon, in the potentially devastating energy of the Cascadia Fault.

Drive along the Pacific Coast from Eureka up through Oregon and Washington, in every coastal town you will see blue Tsunami Evacuation signs posted on every other street corner. Watch television along the coast and you will see frequent Public Service Announcements detailing the potential for a tsunami and answering the musical question: Where you gonna run to now?

After seeing all this from Crescent City to Sequim, you will be telling yourself, “I don’t know what they are waiting for, but I don’t want to be around when it happens.”

If any place along the Pacific Coast is likely to get worked, Crescent City is it. The fishing village has tsunami issues. A 9.2 megathrust earthquake in Chile in 1960 caused a tsunami that did minor damage within Crescent City Harbor. And Good Friday, 1964, was not so good to Crescent City either. The 9.5 Great Anchorage Earthquake generated enough extra energy to send a series of four waves that took just over 4 hours to travel the 2000 miles from Prince William Sound to Crescent City. The first three waves were minor, but the fourth drained the south-facing harbor, then swept over the breakwaters at 20 feet high and 500 MPH. The tsunami sank two dozen fishing boats and devastated 30 city blocks, and dashed lumber, cars and other debris against buildings. The largest wave picked up a gasoline truck and slammed it against electrical wires, starting a fire that spread to the Texaco tank farm, which burned for three days.

What geologists and public safety officials are more than a little worried about is a repeat of a seismic event that is almost buried in the mists of time. On January 26, 1700, a megathrust earthquake along the Cascadia fault of North America generated a tsunami that propagated across the Pacific Ocean, and wreaked havoc on Japan’s Honshu Island. There was no local seismic event to warn coastal residents, and the wave came in from out of deep water and rose to more than 10 meters, destroying coastal villages, sinking ships and sweeping untold numbers of villagers into the sea.

The only witnesses to the incident in North America were Native American tribes from the Haida of the Queen Charlotte Islands to the coastal Pomo of Mendocino. Those who survived the earthquake and the massive tsunamis that followed handed down stories of the giant winter waves that appeared from nowhere, and swallowed villages and villagers. Those foggy myths exist today, but American geologists had only those vague stories, tree rings and weird layers of sand to support a theory that the Cascadia fault let loose with a tremendous earthquake between August 1699 and May 1700.

It was all theory until 1996, when geologists in Japan searching through their nation’s vast archives found written reports of a large tsunami event along the east coast of Honshu Island that was not generated by a local earthquake. In 2003, Keni Satake of the Geologicial Survey of Japan, with Americans Kelin Wang and Brian Atwater, published Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions, which proved the Cascadia fault had produced a 9.0 earthquake in 1700, but also raised a scary question: How likely is that to happen again, and what would the consequences be for the Pacific Basin?