Swarm of Small Quakes off Oregon Coast

NEWPORT, Ore. (AP) _ An earthquake "swarm'' that began last weekend has resulted in thousands of small earthquakes off the Oregon coast in recent days but the size of the quakes did not pose any tsunami threat, officials said.

Scientists from Oregon State University said they are joining National Oceanic and Atmospheric Administration researchers on Saturday for a cruise to investigate a site on the undersea Juan de Fuca Ridge northwest of Astoria called the Endeavor segment.

"These earthquake swarms are associated with seafloor spreading,'' said Robert P. Dziak, an Oregon State oceanographer who works with NOAA at the university's Hatfield Marine Science Center in Newport.

"We suspect what happened was that magma pushed up into the crust and the lava may have broken the surface,'' Dziak said.

The quakes are generally small and not a tsunami threat, although a section of the sea floor off the Northwest coast called the Cascadia subduction zone is similar to the Indian Ocean area that produced a huge earthquake and tsunami that devastated southeast Asia last December.

The much smaller quakes off the Northwest coast generally ranged from magnitude 2 to magnitude 4 and typically occur in swarms during seafloor spreading events, scientists said.

During the first 36 hours of the swarm, nearly 1,500 small quakes were detected. The undersea quake activity was continuing at a "moderate pace,'' Dziak said.

At the Cascadia subduction zone, an oceanic tectonic plate called the Juan de Fuca is pulled and driven (subducted) beneath the continental North American plate, setting up conditions for undersea "megathrust" earthquakes. The Risk >>

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