April 14, 2008

Bizarre Earthquakes Off Oregon Coast

A peculiar swarm of earthquakes have been occurring off of Oregon's central coast, resembling those that happen just prior to a volcanic eruption. However, scientists are baffled as there are no volcanoes in the area.  

There have been more than 600 quakes during the past 10 days in an area 150 miles southwest of Newport. The largest quake was a magnitude of 5.4, with two others measuring greater than magnitude 5.0, OSU reported.

Few of the quakes have been strong enough to be felt on land, and they have not shown the typical pattern of a major shock followed by a series of diminishing aftershocks.

Robert Dziak, a geophysicist for the National Oceanic and Atmospheric Administration and Oregon State University, suspects the quakes could be the result of molten rock rumbling away from the established faults in the area.

The scientists used underwater microphones called hydrophones to listen to the earthquakes.  Dziak told the Associated Press the quakes sound like low thunder on the hydrophones, and are unlike anything scientists have heard in 17 years of listening.   

Some of the quakes have also been detected by earthquake instruments on land.

The hydrophones are left over from a network the Navy used to listen for submarines during the Cold War. The devices were also used to detect passing ships, whales calling out to one another and earthquakes on the ocean's floor.

Dziak said the scientists hope to deploy an OSU research ship to gather water samples, searching for evidence of stirred up sediment and chemicals indicating magma is moving up through the Juan de Fuca Plate.

The Earth's crust is made up of plates that rest on molten rock, known as magma. The plates are constantly rubbing together.   When the magma erupts through the crust it creates volcanoes, which can occur in the middle of a plate. It's possible that such an event would cause the plates lurch against each other, creating earthquakes along the edges.

Off the Oregon coast, the Juan de Fuca Plate is a small piece of crust being crushed between the Pacific Plate and North America, Dziak said.


Image Caption: Satellite imagery of the northeast Pacific Ocean and western North Pacific Plate. Explorer, Juan de Fuca, and Gorda Ridges make up the plate boundary between the Pacific Plate and the Juan de Fuca/ Explorer/ Gorda Plates. The Cascadia Subduction Zone is also highlighted, which is the area where oceanic crust is subducting beneath the North American Plate. Courtesy NOAA


On the Net:

National Oceanic and Atmospheric Administration

Juan de Fuca Plate - Wikipedia

Associated Press