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Just after midnight on Tuesday, a 4.2 magnitude earthquake struck the Oregon coast. It wasn’t groundbreaking because earthquakes always happen on the high seas.
An hour and a half later, another tremor rippled across the seafloor.
And then another earthquake struck. And another. And another.
Until now, seismologists were really paying attention. About 30 earthquakes occurred in the westernmost part of the Blanco Fracture Zone that day. 200 miles long According to incoming data, the plate boundary on state coasts United States Geological Survey. The strongest recorded tremor was 5.8 magnitude and the smallest 3.4.
At least 66 earthquakes were recorded in the area Wednesday afternoon, said Susan Hough, a seismologist with the USGS in Pasadena, California. And the earthquakes did not subside on Wednesday night.
If so many earthquakes had occurred in a different region, like the formidable San Andreas fault in California, there could have been chaos and destruction.
But Don Blakeman, a geophysicist at the USGS National Earthquake Information Center, said these small to moderate earthquakes, known as swarms in earthquake language, are nothing to worry about.
“That’s exactly how the world works at this point,” he said, adding that the area is “a highly active one.”
A person 250 miles away may feel the ground shaking, however, he said he need not worry about a tsunami or a strong earthquake occurring much closer to them.
The National Weather Service has tiredly reminded people of this fact. excitement Wednesday morning.
“For the 7th time in the last 16 hours… Earthquake and tsunami are not expected off the coast of Southern Oregon,” the agency said.
Douglas Toomey, a professor of geophysics at the University of Oregon, said Wednesday that it’s not actually possible for the Blanco Fracture Zone to generate a tsunami.
The Blanco Fracture Zone is known as a strike-slip fault, meaning that its two sides move horizontally side by side. Dr. Toomey, imagine someone ‘rubbing both hands together’. For a tsunami to occur, the seafloor has to slide up or down.
(Other fault types have vertical movement that can create a tsunami.)
While a tsunami is an impossible event throughout the Blanco Fracture Zone, earthquakes occur quite frequently here.
Dr. “If there was a seismometer on the ocean floor there, it would record earthquakes every week,” Toomey said.
He said he was “not entirely surprised” to hear the flock, but added that the number and size of the tremors were “somewhat unusual”.
At the USGS in Pasadena, Dr. A swarm in 2005 may have overshadowed that, but its strongest quake reached a magnitude of 6.6, Hough said. The largest tremor of the herd this week reached a magnitude of 5.8.
While there have been a similar number of shaking swarms in the past as this week, the USGS did not monitor the swarms as closely as they do now.
It wasn’t clear what caused this flock, but Dr. Hough said there is a theory that the swarms could generally be caused by fluids that “moved” after they entered the earth’s crust.
“We don’t really understand why the swarms started,” he said.
It’s hard to predict when a flock will end, but in parts of California it could take a week, he said.
In an earthquake, the stresses along a fault reach the breaking point, releasing a large amount of energy. This can trigger nearby malfunctions, similar to shaking an unopened can of soda.
Dr. Hough said it’s possible, though “highly unlikely,” that the swarm from the Blanco Fracture Zone will mobilize the Cascadia Subduction Zone, located 100 miles to the east.
The Cascadia region, a fault that runs from Northern California to Vancouver Island, is like the larger and scarier cousin of the Blanco Fracture Zone. It is closer to the shore and much longer and would have moved vertically in an earthquake. A strong earthquake there could devastate the Pacific Northwest. seismologists say.
But again, experts said there was no reason to worry about the herd in the Blanco Fracture Zone. But its neighbor to the south is more alarming.
The Blanco zone is the same type of fault as the San Andreas fault in California, but it’s really the only thing they have in common. San Andreas is a long fault that forms the backbone of California and there is a significant earthquake risk along its sections. USGS In California lore, this long-feared earthquake is known as the Big One.
Dr. Hough said that the Blanco Fracture Zone was not expected to produce such a strong earthquake because the earth’s crust is much thinner there than in the San Andreas fault zone.
“It’s a mistake like going through tissue paper instead of cardboard,” he explained.
Henry Fountain contributing reporting.
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