Researchers learn earthquakes intensify in deep sedimentary basin near Fairbanks

New research looks into why earthquakes that move through the Nenana Basin are stronger and longer than in other locations.
Published: Feb. 6, 2023 at 7:10 AM AKST
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FAIRBANKS, Alaska (KTUU) - The tallest peak in North America has nothing on one obscure basin over 100 miles to the northeast.

At nearly 4.5 miles deep, the Nenana Basin extends further in the ground than the crest of Denali (3.85 miles), and it is this property that causes earthquakes to strike longer and harder when they enter the region, according to researchers at the University of Alaska Fairbanks’ Geophysical Institute.

University seismology professor Carl Tape and Ph.D. student Kyle Smith dug up these findings in a recent study in the Bulletin of the Seismological Society of America, which they co-authored.

This map shows the Nenana Basin and Minto Flats fault zone in central Alaska. The color denotes...
This map shows the Nenana Basin and Minto Flats fault zone in central Alaska. The color denotes the depth to the basin's basement surface. The triangles denote seismic stations and include 13 stations that operated from 2015-2019.(UAF Geophysical Institute)

“When earthquake waves enter into these areas like Nenana Basin, they get trapped and they shake longer, and the waves are larger. They kind of slow down and crash into each other,” Tape said. “And that amplifies the waves and so it’s that kind of motion that we’re most interested in.”

Between 2015 to 2019, researchers analyzed data from 48 earthquakes. The earthquakes were recorded by 13 seismic monitors in a part of the basin known as Minto Flats.

“The scientists found that seismometers overlying the basin’s deepest areas recorded stronger low-frequency amplification and that monitors at the basin’s shallow edges recorded minimal amplification as the seismic waves ricocheted inside the basin,” the press release stated. “They also found that higher frequency amplification occurs at monitors over both deeper and shallower areas.”

This means earthquakes are felt more profoundly in the basin, which overlaps the portion of the Tanana River to the north of the community of Nenana.

The Nenana Basin is made up of sedimentary rock that has accumulated over time. According to the research paper, the basin has been filling with gravel from the Tanana River, accounting for almost a mile of rock over the past 6 million years.