Study finds if March 11 Tohoku earthquake struck U.S. northwest coast, it would leave it in ruins

February 23, 2012 – SEATTLE – Studies of last year’s giant Tohoku earthquake and tsunami in Japan suggest that shaking from a Cascadia megaquake could be stronger than expected along the coasts of Washington, Oregon and British Columbia, researchers reported Sunday at the annual meeting of the American Association for the Advancement of Science. Scientists are still unraveling last year’s giant Tohoku earthquake and tsunami in Japan, and some of what they’re finding doesn’t bode well for the Pacific Northwest. Detailed analyses of the way the Earth warped along the Japanese coast suggest that shaking from a Cascadia megaquake could be stronger than expected along the coasts of Washington, Oregon and British Columbia, researchers reported Sunday at the annual meeting of the American Association for the Advancement of Science. “The Cascadia subduction zone can be seen as a mirror image of the Tohoku area,” said John Anderson, of the University of Nevada. Anderson compiled ground-motion data from the Japan quake and overlaid it on a map of the Pacific Northwest, which has a similar fault — called a subduction zone — lying offshore. In Japan, the biggest jolts occurred underwater. The seafloor was displaced by 150 feet or more in some places, triggering the massive tsunami. But in the Northwest, it’s the land that will be rocked hardest — because the Pacific coast here lies so close to the subduction zone. “The ground motions that we have from Tohoku may actually be an indication that there could be much stronger shaking in the coastal areas of British Columbia, Washington and Oregon,” Anderson said. Cities like Seattle, Portland and Vancouver, B.C., are far enough from the coast that they might dodge the most violent hammering. But all of the urban areas sit on geologic basins that can amplify ground motion like waves in a bathtub. –Seattle Times