Fury of underwater earthquakes move us closer to the BIG ONE

A swarm of more than 600 earthquakes — ranging from magnitude 2 to 5.4 — have rumbled in a basin off the central Oregon Coast over the past 10 days, sometimes as often as every few minutes. Although the quakes continue about 173 miles southwest of Newport, their occurrence slowed slightly Friday, according to geophysicist Robert Dziak of Oregon State University’s Hatfield Marine Science Center in Newport and the National Oceanic and Atmospheric Administration. He has been listening to the shaking going on deep under the sea.

“It will probably continue not more than another week or so,” he said.

Dziak didn’t know what the quakes might mean or what is causing them because the seismic activity is occurring at an unusual place: the middle of the Juan de Fuca Plate, away from any major tectonic boundaries.

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






The Earth’s crust is made up of plates that rest on molten rock, which are rubbing together side to side and up and down. When the molten rock, or magma, erupts through the crust it creates volcanoes. That can happen in the middle of a plate. When the plates lurch against each other, they create earthquakes along the edges of the plates.

“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,” Dziak said.

Scientists using underwater microphones have detected the smaller earthquakes, which are between magnitudes of 2.0 and 4.0. At least five of the quakes have been at 5.0 or higher, with the strongest a 5.4 quake that was recorded Monday. A 5.0 tremor also hit on Thursday.

“It’s a pretty strong earthquake. A magnitude 5.0, it would knock books off shelves, and anything not attached to the wall would probably tip over if (the earthquake) was right underneath you,” Dziak said.

The earthquakes weren’t felt ashore because they originated offshore and deep within the ocean.

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This instance of seismic activity also is unusual because it wasn’t in the usual sequence of a major quake followed by aftershocks that decline in intensity.

This is the eighth such swarm off the Oregon Coast in the past 12 years. But the other activity took place on a plate ridge. Scientists hope to send out the OSU research ship, Wecoma, to take water samples, looking for evidence that sediment on the ocean bottom has been stirred up and chemicals in the water that would indicate magma is moving up through the crust, Dziak said.


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