UH OH: New research on Japanese quake ominous for 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.

And remember — earthquake concerns aren’t just for the West Coast, what with recent East Coast shocks, and of course the threat of a big New Madrid quake.

Here’s my earlier post on earthquake preparedness. More here. Plus, some recommended gear. More here. Also, here’s some advice from the LAFD, although their excellent PDF booklet seems to have vanished.

UPDATE: Here’s the LAFD booklet, thanks to reader Tim Ryan.