by Frank Mungeam, KGW.com Staff
Posted on January 26, 2012 at 4:00 PM
Updated today at 5:02 PM
Thursday marked the 312th anniversary of the last, great Cascadia Subduction Zone earthquake to strike the Pacific Northwest, according to researchers at the Oregon Department of Geology.
Scientific research in Oregon, Washington, and Japan indicates that a magnitude 9.0 earthquake struck at 9:00 p.m. on January 26 in the year 1700. The data show the quake was centered about 75 miles offshore.
The quake ruptured along a 600 mile long fault, running from Northern California to Southern British Columbia, causing untold damage and destruction to the Pacific Northwest coast and the Native American tribal communities that made the coast their home.
The destruction caused by the similar magnitude 9.0 earthquake and the tsunami it generated on March 11, 2011, offshore Japan provides a chilling parallel to what could happen here in Oregon.
"The geologic record of these great offshore earthquakes goes back at least 10,000 years," said Ian Madin with the Oregon Department of Geology and Mineral Industries. "We know they occur about every 300 to 600 years, so it is a matter of when, not if, the next one will strike."
Oregon coastal towns are most at risk from a Cascadia Subduction Zone earthquake because of the potentially devastating tsunami the earthquake generates as it ruptures the ocean floor.
Coastal communities from Brookings to Astoria have been developing emergency plans and continue to practice evacuation drills to help those living and working in the tsunami inundation zone - that area where ocean waves would push inland.
"We need all Oregonians to know that strong shaking felt on the coast means to evacuate immediately, and all coastal residents should know where to go and how to get there," said Madin.
