Three-hundred years ago, the Juan de Fuca plate under the ocean in America's Pacific Northwest suddenly slipped beneath the North American plate and forced its way about 60 feet eastward, triggering a massive earthquake that scientists estimate was roughly magnitude 9.0. The quake was so large that the tsunamis it created traveled all the way to the shores of Japan. The Pacific Northwest, which encompasses the cities of Vancouver, Seattle, and Portland, has been relatively stable since then, but scientists familiar with the area theorize that earthquakes with magnitudes greater than 8 may occur there every 400 to 500 years.
To help prepare for such an event, a team of researchers used the supercomputer at San Diego State University to run a "virtual earthquake" program designed to calculate realistic three-dimensional simulations of what a major earthquake could do to the Pacific Northwest. What the scientists learned from their virtual "megaquake" was not exactly reassuring.
With a rupture scenario beginning in the north and propagating toward the south along the 600-mile long Cascadia Subduction Zone, the ground moved about 1.5 feet per second in Seattle; nearly 6 inches per second in Tacoma, Olympia, and Vancouver; and 3 inches per second in Portland. Given the fact that Seattle, Tacoma, and Olympia are all built on sediment-filled geological basins that are prone to amplifying the waves generated by a major earthquake, the long-duration shaking and high ground velocities could inflict major damage on those metropolitan areas.
