Constant Seismic Activity Found Off Oregon Coast

Using hand-me-down technology from the Cold War, scientists have discovered that the seafloor off the Pacific Northwest is a jumping kind of place, with thousands of small, swarming earthquakes and tectonic plates that are slowly rearranging themselves.

The findings could mean that a "Big One" earthquake may not be as severe as previously thought, the lead researcher said.

An article in the journal Geology by researcher Robert Dziak describes the findings. Dziak is an associate professor at Oregon State University who also works for the National Oceanic Atmospheric Administration. He's stationed at OSU's Hatfield Marine Science Center in Newport.

Dziak's article describes both new data and a record of earthquakes going back more than a decade.

Much of the data was collected using once-secret Cold War "hydrophones" the Navy uses to track submarine movements in the Pacific Ocean. Dziak said the Navy provides controls the system of seafloor microphones and relays the data to Newport.

Dziak says the evidence is that multiple tectonic plates off the Pacific Northwest appear to be rearranging themselves.

The plates have been slowly jamming into each other. Dziak said one boundary among them appears to be turning into a fault that's more like the San Andreas Fault to the south in California. Instead of ramming together, the plates are rubbing past each other, he said.

Emphasizing that the conclusions are tentative, Dziak said the consequence could be a shortening of the fault along the Pacific Northwest, so a major earthquake wouldn't be so extensive or severe.

The rearrangement could limit the potential for a magnitude 9 earthquake, he said.

"It would still ruin our day, but it wouldn't be quite so bad," he said.

Dziak also said that the hydrophone project has turned up evidence of intense earthquake activity, intense clusters of quakes that previously had gone undetected.

These are associated with underwater volcanic activity and are like the swarms of earthquakes that can precede volcanic eruptions such as that at Mount St. Helens.

The quakes were small, on the order of magnitudes 2-4, but numerous, Dziak said, with as many as a thousand of them in a three-week period.