Mapping Near-Surface Rigidity Structure Using Co-Located Pressure and Seismic Sensors From the Earthscope Transportable Array

Date: 4/26/2019

Time: 02:30 PM

Room: Pine

The coupling between the atmosphere and the solid Earth is strong for frequencies between 0.01 Hz and 0.05 Hz. In this frequency band, when the surface pressure is large, the atmosphere-generated seismic noise completely dominates the ocean-generated noise. By adopting the homogeneous half-space model by Sorrells (1971) and following the theoretical work by Tanimoto and Wang (2018), we estimated rigidity at 801 stations in the EarthScope Transportable Array (TA) by studying the atmosphere-ground coupling. We compute the ratio between the horizontal seismic power spectral density (PSD) and the (co-located) pressure PSD at 0.02 Hz, and this ratio reflects how much the ground responds to the surface pressure. Soft medium has higher seismic PSD amplitude in comparison to hard medium under the same pressure, thus has higher ratios; from this ratio, we can determine the shallow elastic structure.

We select one-hour-long horizontal seismic and pressure data with coherence higher than 0.7, and thus obtain robust estimates for rigidity. Our approach in this study focuses on the analysis of the horizontal-component seismic data, which differs from our previous work (Tanimoto and Wang, 2018).

We determined rigidity at 801 TA stations that are available since 2012. The resulting rigidity on the dense station map shows good spatial agreement with large-scale surface geology. Among them, 31 most rigid stations are in Alaska; many other high rigidity stations are in the Appalachian Mountains area. Both regions are known for having hard rocks. Low rigidity stations are located along the Mississippi Alluvial Plain, where soft sediments are found. Our method provides a simple and cost-effective way to retrieve near-surface structure by using stations with co-located seismic and pressure sensors.

Presenting Author: Jiong Wang

Authors