The Nenana Basin lies southwest of Fairbanks. The Parks Highway runs along its eastern boundary, and the Tanana River runs right through the middle of it. The basin is 56 miles long and 7.5 miles wide. Over the course of millions of years, the basin has been filled in with river sediment. Considering that the basin is 4 miles deep (7km), that is a lot of fill.
Several entities have been drilling test holes throughout the basin looking for oil and gas, so the University of Alaska – Fairbanks has been studying the basin’s makeup. One thing they found is that earthquakes last longer and feel a lot stronger in the basin, than just outside the basin.
The shockwaves from an earthquake travel differently through the sediment, which is mostly gravel, than the solid rock along the ridge lines. Reverberation also plays a roll here: The seismic waves are amplified by the basin walls and floor.
Seismic sensors have verified what local residents have been claiming: The shaking is a lot worse down in The Flats than up in the hills.
Source credit: Alaska Public Media, University of Alaska – Fairbanks