Kenai Lake is pretty placid. But right after the 1964 Good Friday earthquake, the lake was hit with a tsunami that washed out the bridge there and left behind blocky layers of sediment.
Those layers are useful today to scientists who are looking to learn more about past and future earthquakes.
Like Peter Haeussler. He’s a research geologist for the U.S. Geological Survey, based in Alaska. He spoke to a crowd in Cooper Landing this week about his research on earthquakes in the area.
“It actually was studies of the 1964 earthquake that kind of gave birth to modern earthquake detectives,” he said.
Earthquake detectives want to learn more about when large earthquakes occured, in part to brace for the future. Engineers need to know more about how the ground shakes so they can build infrastructure that’s up to the task.
One way to get that information is through paleoseismology.
"'Paleo' means ancient, and 'seismology' means earthquakes. So it’s understanding the frequency of old earthquakes through studying lakes," Haeussler said.
Sediment on the sides of lakes, like Kenai Lake, gets shaken up during big earthquakes. It then floats to the bottom and settles in layers.
Geologists can dig out cores from the bottom of those lakes to glean snapshots of the events that occurred nearby, in the last 90 years or so. They do that by sticking what’s essentially a long tube into the ground to get a cross section of rocky layers.
They can also use what’s called a “chirp,” which releases sound waves to reflect the different layers below the bottoms of lakes.
“One thing that we really like about 'em is that they have annual laminations," Haeussler said. "And these are often called varves, and they’re a lot like tree rings. You have almost a yearly record of sedimentation into a lake, based on these things.”
Drake Singleton is a Mendenhall Fellow with the U.S. Geological Survey. He said that information is really helpful.
While geologists can’t predict exactly when earthquakes will occur, they can use the information to develop hazard maps for engineering purposes.
“As scary as it is to go through an earthquake of this magnitude and the strong shaking, these events are really good tools for us to understand the response to geology," Singleton said.
The research isn’t without its logistical challenges.
"Last year, we were coring, over in this part of the lake, and we actually got a fish inside our core tube," Haeussler said.
The Geological Survey is going to take cores from Kenai and Skilak lakes to a lab to learn more about the 2018 Southcentral earthquake.
Haeussler said a lot of the cores taken in the past are stored in the old Sam’s Club building in Anchorage. That core library includes a cutting from the first Prudhoe Bay discovery well, he said.