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QUAKES, WAVES COULD CLOBBER THE NORTHWEST

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Scientists studying a 1992 California earthquake reported evidence Friday that the Pacific Northwest - from Cape Mendocino to British Columbia - is at risk for catastrophic temblors and sea waves.

In the journal Science, 20 reseachers who spent a year analyzing data from the April 1992 tremor in Humboldt County in northern California said this was not just any earthquake but the much-feared spasm in the "Cascadia subduction zone" that tore the crust six miles under the surface.The finding could provide conclusive proof that far larger shakers may eventually jar territory stretching from Cape Mendocino - already among California's most seismically active areas - into Canada, a region historically devoid of strong tremors.

The future earthquake "could generate a tsunami, or sea wave, powerful enough to inundate communities along much of the Pacific Northwest coast within minutes of the main shock," said David Oppenheimer of the U.S. Geological Survey regional center in Menlo Park.

What is new about the scientists' findings, he said, "is that this is the first time we have seen a bona fide subduction earthquake in the area."

In subduction earthquakes - among the largest in the world - plates in the Earth's crust lunge sharply as they are shoved, or subducted, under other plates.

These temblors - such as the jolt on the coast of Chile in 1960 that measured 9.5 on the Richter scale, perhaps the largest in recorded history - generate tsunamis that can reach 30 feet or more, wreaking havoc and destruction.

The 7.1 quake in 1992, which because it occurred at low tide set off only a minor tsunami, occurred near a geologically complex formation called "the Mendocino Triple Junction."

Here, the infamous San Andreas Fault ends against a small slab of crust called the Gorda Plate, which - pushed by the larger Pacific Plate - is sliding under the edge of the North American continent.

The Gorda Plate and the larger Juan de Fuca Plate to its north are disappearing into the Cascadia subduction zone, named for the Cascade Range of volcanoes that includes Mount Shasta, Mount Hood and Mount St. Helens.