Layered Structure and Vs30 at Colocated Pressure and Seismic Stations in the Transportable Array

Jiong Wang, & Toshiro Tanimoto

Published August 15, 2020, SCEC Contribution #10672, 2020 SCEC Annual Meeting Poster #039 (PDF)

In this study, we present layered structure and Vs30 at many Transportable Array (TA) stations by performing an inversion approach with low-frequency seismic noise generated by surface pressure changes. The main source of seismic noise below 0.05 Hz is usually atmospheric pressure variations, especially when surface pressure variations are large. The amount of ground deformation under surface pressure loadings reflects the characteristics of shallow elastic structure. If a surface station is colocated with seismic and pressure sensors, shallow rigidity can be estimated by using the ratios between seismic and pressure data. We adopt Sorrells’ half-space model (1971), with a propagating pressure waves assumption. In a previous study, we estimated half-space elastic structure at 784 Transportable Array (TA) stations. Furthermore, we developed an inversion approach to estimate layered structure using seismic and pressure data at different frequencies below 0.05 Hz. In the inversion scheme, we utilize surface observable η(f)=Sz/Sp, where f is frequency and Sz and Sp are the power spectral densities of vertical seismic data and of surface pressure data. A vertically heterogeneous medium is assumed beneath a station where density, P wave velocity, and S wave velocity change with depth. Using numerical differentiation, we derive depth sensitivity kernels for η(f) with which we invert η(f) for shallow structure. Depth sensitivity is typically controlled by elasticity in the uppermost 50-100 meters. We estimated layered structure at 9 colocated stations in the Piñon Flat Observatory. Our estimates of Vs30 agree with both an independent estimate of Vs30 on the site (Yong et al., 2016) and are consistent with knowledge of local geology. Although estimated layered structures are much smoother compared to the velocity profile obtained by the active-source survey, our method is still sufficient for estimates of Vs30 because Vs30 is an averaged quantity for the uppermost 30 meters. We will present Vs30 at many TA stations estimated from the inversion approach.

Citation
Wang, J., & Tanimoto, T. (2020, 08). Layered Structure and Vs30 at Colocated Pressure and Seismic Stations in the Transportable Array. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology