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Unusual Earthquake Swarm Off Oregon Coast Puzzles Scientists

Oregon coast. Researchers have recorded more than 600 earthquakes in the last 10 days off the central Oregon coast in an area not typically known for a high degree of seismic activity. (Credit: iStockphoto/S. Greg Panosian)

Oregon, USA

More than 600 earthquakes in the last 10 days off the central Oregon coast are occurring in an area not typically known for a high degree of seismic activity. This earthquake “swarm” is UNIQUE because it is occurring within the middle of the Juan de Fuca plate – away from the major, regional tectonic boundaries. “In the 17 years we’ve been monitoring the ocean through hydrophone recordings, we’ve never seen a swarm of earthquakes in an area such as this. We’re not certain what it means. But we hope to have a ship divert to the site and take some water samples that may help us learn more.” The water samples may indicate whether the process causing the earthquakes is tectonic or hydrothermal. At least three of the earthquakes have been of a magnitude of 5.0 or higher which also is UNUSUAL. On Monday (April 7), the largest event took place, which was a 5.4 quake. Seismic activity continued through the week and a 5.0 tremor hit on Thursday (April 10). Numerous small quakes continued in-between the periodic larger events. The earthquakes are located about 150 nautical miles southwest of Newport, in a basin between two subsurface “faulted” geologic features rising out of the deep abyssal sediments. The hill closest to the swarm location appears to be on a curved structure edging out in a northwestern direction from the Blanco Transform Fault toward the Juan de Fuca ridge. “Some process going on down there is sustaining a high stress rate in the crust...The fact that it’s taking place in the middle of the plate, and not a boundary, is puzzling. It’s something worth keeping an eye on.”

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