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Pacific Northwest At Risk For Mega-Earthquake
Hugh Pickens writes "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 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 might 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.'" Read below for more.
The last major earthquake to hit the Cascadia Subduction Zone was in January 1700. 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% 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."
The last major earthquake to hit the Cascadia Subduction Zone was in January 1700. 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% 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."
But it's not pure extrapolation. Earthquakes in subduction zones are the result of pressure buildup. They are not spaced randomly, as the time between them is determined by the tectonic action that causes the pressure to be generated or released. Thus, the time difference between earthquakes is relevant.
I hate printers.
If you live in the Pacific Northwest, there's a good chance that your house *is* built to at least some earthquake code. My house was built in 1960, has metal tie plates, and is bolted to the foundation, and not as a retrofit.
This isn't exactly new knowledge that earthquakes happen close to active volcanos, you know.
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