Dozens of earthquakes hit Oregon coast, but experts say not to worry

Just after midnight Tuesday, a magnitude 4.2 earthquake struck off the coast of Oregon. It was not revolutionary, because earthquakes h...


Just after midnight Tuesday, a magnitude 4.2 earthquake struck off the coast of Oregon. It was not revolutionary, because earthquakes happen all the time offshore.

An hour and a half later, another tremor rocked the seabed.

And then another earthquake hit. And another. And another.

Now the seismologists were really paying attention. Almost 30 earthquakes occurred that day along the westernmost segment of the Blanco Fracture Zone, approximately 200 miles long border of the plate off the state coast, according to data from the United States Geological Survey. The strongest earthquake recorded had a magnitude of 5.8, the smallest of 3.4.

As of Wednesday afternoon, at least 66 earthquakes had been recorded in the area, said Susan Hough, a seismologist at the USGS in Pasadena, Calif. And the earthquakes had not stopped Wednesday night.

If so many earthquakes had struck a different area, like the formidable San Andreas Fault in California, there could have been chaos and destruction.

But this series of small and moderate earthquakes, known in earthquake parlance as a swarm, was nothing to worry about, said Don Blakeman, a geophysicist at the USGS National Earthquake Information Center.

“This is exactly how the land works there,” he said, adding that the area was “a fairly active area”.

Someone on the beach 250 miles from the fault could feel the ground shaking, he said, but would not have to worry about a tsunami or a powerful earthquake occurring much closer to it. ‘them.

The National Weather Service has wearily reminded people of this fact on Twitter Wednesday morning.

“For the 7th time in the past 16 hours… a tsunami is not expected with an earthquake off the southern Oregon coast,” the agency wrote.

In fact, the Blanco Fracture Zone is extremely unlikely to generate a tsunami, said Douglas Toomey, professor of geophysics at the University of Oregon on Wednesday.

The Blanco fracture zone is what is called a stall fault, which means that its two sides move horizontally next to each other. Think about when someone “rubs both hands,” Dr. Toomey said. For a tsunami to occur, the seabed would have to move up or down.

(Other types of faults move vertically, which could generate a tsunami.)

While a tsunami is an impossible event along the Blanco Fracture Zone, earthquakes are quite common there.

“If they had an ocean floor seismometer, it would record earthquakes every week,” Dr Toomey said.

He said he was not “entirely surprised” to hear of the swarm, but added that the number and size of the tremors were “a little unusual”.

A 2005 swarm may have eclipsed this one, however, as its most powerful quake reached a magnitude of 6.6, said Dr. Hough of the USGS in Pasadena. The biggest quake in the swarm this week reached a magnitude of 5.8.

While there may have been swarms in the past that generated a similar number of tremors as this week, the USGS did not monitor the swarms as closely as they are today.

The cause of this swarm was not clear, but Dr Hough said there was a theory that swarms in general could be caused by fluids that “move” once they enter the earth’s crust. .

“We don’t really understand why the swarms are starting,” she said.

It’s hard to predict when a swarm will end, but it can last for a week in parts of California, she said.

In an earthquake, the stresses that have built up along a fault reach a breaking point, releasing enormous amounts of energy. It can trigger nearby rifts, like knocking over a row of dominoes.

It is possible, although “extremely unlikely,” that the Blanco Fracture Zone swarm could trigger the Cascadia Subduction Zone, located 100 miles to the east, Dr Hough said.

The Cascadia Zone, a fault line stretching from northern California to Vancouver Island, is like the Blanco Fracture Zone’s larger and spookiest cousin. It is closer to the coast and much longer, and it would move vertically during an earthquake. A powerful earthquake could devastate the Pacific Northwest, seismologists to say.

But, again, experts said there was no reason to be concerned about the swarm along Blanco’s fracture zone. Its neighbor to the south, on the other hand, is more worrying.

The Blanco area is the same type of fault as the San Andreas fault in California, but that’s really all they have in common. The San Andreas is a long fault that runs up the spine of California, and there is a significant earthquake risk along parts of it, according to the USGS In California lore, this dreaded earthquake is known as the Big One.

The Blanco Fracture Zone is not expected to generate such a powerful earthquake because the earth’s crust is much thinner there than in the San Andreas Fault area, Dr Hough said.

“It’s like a rift running through a piece of tissue paper,” she explained, “as opposed to cardboard.”

Henri fountain contributed reports.



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Newsrust - US Top News: Dozens of earthquakes hit Oregon coast, but experts say not to worry
Dozens of earthquakes hit Oregon coast, but experts say not to worry
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