Supercomputer models 9.0 megaquake in Pacific Northwest

On January 26, 1700, at about 9 p.m. local time, the Juan de Fuca plate beneath the ocean in the Pacific Northwest suddenly moved, slipping some 60 feet eastward beneath the North American plate in a monster quake of approximately magnitude 9, setting in motion large tsunamis that struck the coast of North America and traveled to the shores of Japan.

Scientists believe that earthquakes with magnitudes greater than 8, so-called ‘megathrust events,’ occur along this fault on average every 400 to 500 years.

To model the impact of such a disaster, researchers at the University of California - San Diego have used a supercomputer-driven ‘virtual earthquake’ to explore likely ground shaking in a magnitude 9.0 megathrust earthquake in the Pacific Northwest.

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 in Portland, Oregon. Additional simulations, especially of earthquakes that begin in the southern part of the rupture zone, suggest that the ground motion under some conditions can be up to twice as large.

The long-duration shaking, combined with high ground velocities, raises the possibility that such an earthquake could inflict major damage in metropolitan areas - especially on high-rise buildings in downtown Seattle. Compounding the risks, like Los Angeles to the south, Seattle, Tacoma, and Olympia sit on top of sediment-filled geological basins that are prone to greatly amplifying the waves generated by major earthquakes.

In addition to increasing scientific understanding of these massive earthquakes, the results of these simulations can also be used to guide emergency planners, to improve building codes, and help engineers design safer structures.

The researchers are now planning to conduct additional simulations to explore the range of impacts that depend on where the earthquake starts, the direction of travel of the rupture along the fault, and other factors that can vary.

This research was supported by the National Science Foundation, the US Geological Survey, the Southern California Earthquake Center, and computing time on an NSF supercomputer at SDSC.

•Date: 28th February 2008• Region:US •Type: Article •Topic: DR general
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