Quakes off Oregon coast stump scientists

by Michael Milstein, The Oregonian
April 11, 2008

Geologists at Oregon State University are preparing to divert a research ship to investigate an unusual offshore swarm of earthquakes - including three of magnitude 5 or larger - about 170 miles southwest of Newport.

The earthquakes started about 10 days ago and are continuing, although they appeared to taper off slightly Thursday night, said Robert Dziak, an OSU marine geologist in Newport. Instruments have recorded more than 600 tremors, many of them very small.

The quakes are puzzling because they are not occurring along the edge of the tectonic plates that make up the Earth's crust, where geologists are used to seeing seismic activity. Instead, they're centered in the Juan de Fuca Plate, a span of crust off the Northwest Coast, about 40 miles from the plate's edge.

The largest earthquake was a magnitude 5.4 tremor on Monday. A magnitude 5 quake hit Thursday. the rest