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Estimation of Vs30 at the EarthScope Transportable Array Stations by Inversion of Low-Frequency Seismic Noise
  • Jiong Wang,
  • Toshiro Tanimoto
Jiong Wang
University of Chicago

Corresponding Author:jiongwang@uchicago.edu

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Toshiro Tanimoto
University of California, Santa Barbara
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One of the main sources of seismic noise below 0.05 Hz is the atmospheric pressure variation, especially when surface pressure variations are large. The amount of ground deformation under surface pressure variations reflects the characteristics of shallow elastic structure. When a surface broadband seismic stations is equipped with a pressure sensor, we can estimate near-surface shear-modulus structure using an inversion method. In the inversion method, we have the surface observable η(f)=Sz/Sp, where f is a frequency between 0.01 and 0.05 Hz, and Sz and Sp are the power spectral densities of vertical seismic data and of surface pressure data. We derive depth sensitivity kernels for η(f) with which we invert for elastic moduli of the shallow structure. Between 0.01 and 0.05 Hz, sensitivity kernels typically have peaks at depths within the uppermost 100 meters. Based on vertically heterogeneous 1-D structures, we estimate Vs30 at 744 USArray Transportable Array stations. Vs30 is the time-averaged shear-wave velocity from the surface to the 30-meters depth. We compare our results with various surficial geology maps. Although Vs30 has high horizontal variability over a short distance on the scale of hundreds of meters, we find correlations between Vs30 and large-scale geological structures, such as mapped units and surficial materials. We find good agreement between estimated Vs30 and mapped Quaternary sediment depths, where stations with thicker underlying sediment tend to have slower Vs30.
Apr 2022Published in Journal of Geophysical Research: Solid Earth volume 127 issue 4. 10.1029/2021JB023469