Pacific Northwest At Risk For Mega-Earthquake

jrholliday's picture

Science Daily Headlines reports on research by Oregon State University marine geologist Chris Goldfinger showing that earthquakes of magnitude 8.2 (or higher) have occurred 41 times during the past 10,000 years in the Pacific Northwest. By his extrapolation, there is a 37% chance of another major earthquake in the area in the next 50 years that could exceed the power of recent seismic events in Chile and Haiti. If a magnitude-9 quake does strike the Cascadia Subduction Zone, extending from northern Vancouver Island to northern California, the ground could shake for several minutes, highways could be torn to pieces, bridges may collapse, and buildings would be damaged or even crumble. If the epicenter is just offshore, coastal residents could have as little as 15 minutes of warning before a tsunami could strike. 'It is not a question of if a major earthquake will strike,' says Goldfinger, 'it is a matter of when. And the "when" is looking like it may not be that far in the future.'

The last major earthquake to hit the Cascadia Subduction Zone was in January of 1700, and scientists are aware of the impact because of written records from Japan documenting the damage caused by the ensuing tsunami, which crested across the Pacific at about 5 meters (15 feet). Knowledge about what happened in Oregon and Washington is more speculative, but the consensus — gleaned from studies of coastal estuaries, land formations, and river channels — is that the physical alteration to the coast was stunning. The outer coastal regions subsided and drowned coastal marshlands and forests, which were subsequently covered with younger sediments. "Perhaps more striking than the probability numbers is that we... have already gone longer without an earthquake than 75 percent of the known times between earthquakes in the last 10,000 years," says Goldfinger. "And 50 years from now, that number will rise to 85 percent."


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