Seismic Response of Nenana Sedimentary Basin, Central Alaska

Session: Advances in Upper Crustal Geophysical Characterization
Type: Oral
Date: 4/29/2020
Time: 04:30 PM
Room: 215 + 220
Description: 

We analyze the interaction between the seismic wavefield and large-scale sedimentary basins by focusing on Nenana basin, a several-km-thick, narrow sedimentary basin overlying the Minto Flats fault zone in central Alaska. Seismic stations, including the temporary FLATS network and EarthScope's Transportable Array, record regional earthquakes as well as continuous ambient noise. We quantify the influence of Nenana basin on the seismic wavefield using three data sets: (1) spectral ratios between basin stations and non-basin stations for the same earthquakes, (2) earthquake ground motion metrics for 43 crustal and intraslab earthquakes and (3) ambient noise amplitudes of 7 basin stations relative to a non-basin reference station. For all analyses we examine how quantities vary with the frequency content of the seismic signal and with the basin depth at each station. Seismic waves from earthquakes and from ambient noise are amplified within Nenana basin. At low frequencies (0.1–0.5 Hz), ambient noise ratios and earthquake spectral ratios are in general agreement, with power amplification of 8–14 dB, corresponding to amplitude amplification factors of 2.5–5. At high frequencies (0.5–4.0 Hz), the basin amplifies the earthquake wavefield by similar factors. Our results indicate stronger amplification for the deeper basin stations and weaker amplification near the margins of the basin. Future work devoted to three-dimensional wavefield simulations and to treatment of source and propagation effects should improve the characterization of the frequency-dependent response of Nenana basin to recorded and scenario earthquakes in the region.

Presenting Author: Kyle Smith

Authors