On July 29, 2021, an earthquake struck Chignik, Alaska, registering at an 8.2 magnitude – making it the strongest earthquake that has struck the U.S. in nearly 60 years.
Jeffrey Freymueller, a professor in the department of Earth and environmental sciences at Michigan State University, first started studying the region in 1995.
“That’s kind of how I got into this particular place,” he said.
Earthquakes occur when tectonic plates, which make up Earth’s crust, shift.
Freymueller works on measuring the motion and deformation of the Earth, which includes plate movements, volcanism and investigating active faults.
Using highly precise GPS surveying to measure the position of points on land over time, Freymueller said "we can actually watch how they move, and then use that information to figure out what's going on inside the Earth that's actually causing those motions."
What Freymueller and his colleagues hope to figure out is what exact part of the interface between the two plates slipped, how much it slipped, and relate that to what they observed before the earthquake. Ultimately, they want to determine the patterns of earthquakes and how large the biggest potential earthquake could be in a region.
“The earthquake in general was caused by the Pacific Plate basically shoving underneath North America,” Freymueller said. “That Pacific Plate is moving about six centimeters per year, which would be on the order of two and a fraction inches per year, northward.”
This process is what ultimately resulted in the line of active volcanoes that are present all along the Alaska Peninsula and the Aleutian Islands. It is also responsible for the biggest earthquakes on the planet.
“The reason that we have earthquakes is that, for a lot of time, the contact between two plates is stuck together by friction, just like if you had a heavy object that you're trying to drag across the carpet,” Freymueller said. “There's a lot of frictional force that would resist the motion.”
Tremendous earthquakes are caused by a substantial contact patch that is stuck together by friction. When the earthquake happens, that friction is broken, and there's a sudden motion.
“We're trying to learn some things specific to the region as well as some things that are more generally related to how those kinds of faults behave,” he said.
With this earthquake, one of the questions Freymueller and his team are investigating is why it didn’t generate much of a tsunami.
“Tsunamis are generated usually when there's some kind of a displacement of the seafloor, so some part of the seafloor goes up or down,” he said. “That is actually caused by the motion of the earthquake, not the seismic waves, not the shaking, but the placement associated with the earthquake.”
This earthquake didn't generate much displacement of the seafloor because the earthquake stopped at a relatively deep depth.
“It was probably on the order of 20 kilometers under the surface, which is about 12 miles below the surface,” Freymueller said. “So why did it stop there? Why didn't it continue all the way up to the surface? That is what we don’t know the answer to, yet.”
If there were an earthquake of a shallower depth that occurred in the same location, it would be likely to generate a large tsunami that could be damaging to even the West Coast of the U.S.
“It's not just a local concern, but it could become a concern for Hawaii, for the West Coast, and so on,” Freymueller said. “We also want to understand better what the risks are, what the hazards are, and be able to provide that kind of information so that some kind of hazard assessment can be made.”
These big earthquakes are a major redistribution of forces within the Earth. When the interface is stuck, the overriding plate, which would be North America in this case, gets compressed and pushed backward. The process is similar to loading up a spring.
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“The interface gets compressed, and then when the earthquake happens, it springs back," Freymueller said. “That results in a pretty substantial redistribution of internal forces within the Earth, and the Earth actually responds to that change. We see not just the earthquake, but we see the earthquake and things that happen after it.”
Starting next year, there will be about six new research sites off the coast of Alaska. It will take a few years before Freymueller and his team have enough data from those sites to do anything with it, but the prospects and enthusiasm are promising.
“You can’t pass up those opportunities," he said.
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