Inside Anchorage’s big 2018 earthquake, a ‘Snickers bar’ of shifting layers

A sediment core from the bottom of Eklutna Lake taken by U.S. Geological Survey and Ghent University researchers in February 2019 showing sediment deposit caused by the 2018 M7.0 Anchorage earthquake. (Screenshot from Maarten Van Daele/Ghent University video below)

A year ago, the most impactful earthquake to hit Alaska in half a century damaged buildings and roads in Southcentral, scared a lot of people, changed water levels and stream flow and even caused underground soil liquefaction that resulted in “sand boils” at the surface.

Scientists analyzing all of that and more have been publishing research papers about the magnitude 7.1 Anchorage earthquake, including a multidisciplinary study by more than a dozen authors that’s in the journal Seismological Research Letters.

Geologist Peter Haeussler with the U.S. Geological Survey is one of the dozen or so authors.

He said those types of “intra-slab” earthquakes tend to leave fewer clues at the surface and therefore researchers have to use unique methods for figuring out how often they occur and how big they can be.

“By looking at sediment cores from lake bottoms, you can actually figure out how far back in time you’re actually looking,” Haeussler said. “There are some sort of strange looking sediments that’re thicker and they have physically distinctive features, called turbidites, and there’s strong evidence that turbites were triggered in strong ground shaking in ancient earthquakes in the past.”

Turbidites found in Eklutna Lake, north of Anchorage, after the Nov. 30, 2018 earthquake gave researchers another example of a known earthquake, helping to calibrate measurements on how often the quakes occur.

Haeussler spoke to Alaska Public Media’s Casey Grove.

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Team of U.S. Geological Survey (Alaska Science Center) and Ghent University (Renard Centre of Marine Geology) researchers collecting sediment cores from Eklutna Lake in February 2019, in order to trace the sedimentary imprint of the 2018 M7.0 Anchorage earthquake. (Maarten Van Daele/Ghent University video)