Tuesday, January 26, 2010

North American Quake and Japanese Tsunami: 1700

"Jan. 26, 1700: Northwest Quake Unleashes Trans-Pacific Tsunami"
This Day in Tech, Wired (January 25, 2010)

"1700: A massive earthquake strikes the Pacific Northwest coast, sending a tsunami racing across the ocean all the way to Japan.

"The earthquake was likely around magnitude 9 and occurred in the Cascadia Subduction Zone. The oceanic crust there is being forced beneath the North American Plate along 680 miles of the coastline between Mendocino in northern California and Vancouver Island in British Columbia. Subduction zones are capable of generating the largest earthquakes on Earth, including the 2004 magnitude 9.2 in Sumatra that caused the devastating Indian Ocean tsunami.

"Scientists were able to pinpoint the precise date of the 1700 earthquake using tree rings in ghost forests along the coast...."

There's another large graphic with the article, showing how the wave was spreading across the Pacific.

The article quotes (in translation, happily) Japanese records of the 6-foot waves that flooded fields, caused loss of life and fires, and sank tons of rice in a shipping accident.

The Wired article should be a wake-up call for city governments from about Washington State northwards.

"...The Cascadia Subduction Zone is still active and will generate more major earthquakes in the future. Scientists have found that at least seven earthquakes around magnitude 9 have occurred over the last 3,500 years, an average of one every 500 years. But recent research has shown that many magnitude 8 quakes have shaken the area in the intervening years, bringing the average time between quakes down to 270 years...."

There hasn't been a major quake in that area for the last 300 years. Buildings in cities like Portland aren't necessarily designed to stand a major jolt. It's not hopeless: buildings can be retrofitted. But the time to do it is before the next 9.0 quake hits.

And now, a not-entirely-unrelated post:

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