More than 2,600 aftershocks reveal what took place during large Southcentral earthquake
As aftershocks continue, now to more than 2,600, researchers are learning new information about what happened Friday morning when the Earth shook below Southcentral.
Mike West, state seismologist with the Alaska Earthquake Center calls this group of earthquakes a "rupture patch." West explains you have to look at the area in a three-dimensional view to understand what happened Friday. The earthquake wasn't just 5 to 10 miles north of Anchorage, it was also 25 miles beneath the Earth's surface in a zone where the Pacific plate is being forced underneath Alaska, which sits on the North American plate.
The aftershocks tell researchers at the Alaska Earthquake Center a number of things:
1. They know the earthquake was located inside the Pacific tectonic plate being pulled under Alaska.
2. The earthquake began deep, then ruptured toward the surface of the Earth and to the north.
3. The rupture made it all the way to the top of the Pacific plate, which was once the seafloor.
Researchers will continue to review the aftershocks, learning more about the size and location of the rupture, leading to more understanding about earthquakes in Alaska.
The U.S. Geological Survey estimates more aftershocks are likely. Geologists say within the next week there is greater than a 99 percent chance we'll see between 38 and 84 earthquakes of magnitude 3 or higher re-invigorated by a larger aftershock.
They say the chance of an earthquake of magnitude 5 or higher is 44 percent, though the likelihood of a magnitude 6 or higher is just 6 percent.
West says the aftershocks should begin to taper off in the coming days.
"What — in a normal situation — would happen is the amount of time between those earthquakes would, you know, instead of coming every hour or two, as they have been over the last day, they would stretch out in time and eventually over the course of months begin to, for lack of a better term, fade into the background seismic activity that people are accustomed to feeling in Southcentral," West said.
The aftershocks with Friday's earthquake have been unsettling. Each one is a reminder that you're never quite sure when the next one will strike.
"There’s nothing we can do that can alleviate that or remove it," West said. "But do be aware that the vast majority of aftershocks will be, and have been, much smaller and have not necessarily had, you know, the same kind of impact as Friday morning."
The 1964 earthquake also happened on a Friday, but West says this latest quake was closer in size and movement to the one many Alaskans felt during the night in January 2016.
"I point that out because it was actually a strikingly similar earthquake same basic magnitude and the same basic, you know, mechanical properties going on that generated it. The thing that set it apart is that it was, you know, 150 miles away instead of five or 10," West said.
The Alaska Earthquake Center is charged by the state legislature to research and monitor the state's earthquakes to ultimately reduce Alaska's vulnerability to earthquakes.
West says he doesn't have any words of consolation to put everyone at rest as Southcentral continues to feel aftershocks — only that Alaskans have always known the potential for earthquakes.
"We know that there is a chance out there in the future, whether it’s next week or whether it’s 10 years from now or 100 years from now, that there will be equally or frankly more damages earthquakes." he said. "But yet, the occurrence of yesterday’s earthquake doesn’t actually have a huge impact on our level of readiness. We should’ve already been on this before yesterday’s earthquake."
Seventy-five percent of all earthquakes in the United States with magnitudes larger than five happen in Alaska.
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