Shallow Elasticity Structure from Colocated Pressure and Seismic Stations in the Pinyon Flat Observatory and Estimation of Vs30

Toshiro Tanimoto, & Jiong Wang

Submitted February 6, 2020, SCEC Contribution #10026

The algorithm for deriving shallow elasticity structure from colocated pressure and seismic instruments is applied to data at nine stations in the Pinyon Flat Observatory (PFO) in Southern California. Depth resolution kernels indicate that this approach can recover near-surface rigidity structure in the upper 50-100 m of the Earth. Vs30 for the obtained structure agrees with an independent result by Yong et al. (2016) at the closest station (BPH01). Vs30 derived from the borehole S-wave speed model by Fletcher et al. (1990) also agrees with estimates at nearby locations, considering the size of uncertainties. Derived structures are much smoother than their models, however. This is because our method analyzes slow quasi-static deformation of solid Earth in the frequency range 0.005-0.05 Hz that inherently limits depth resolution. Lack of detailed variations in structures does not seem to be a problem for estimating Vs30 as
Vs30 is an averaged quantity from the upper 30 m of the Earth. Also our estimates are not affected by different choices of frequency range in the inversion. However, our method may have some difficulty at stiff, hard-rock sites because ground deformation caused by surface pressure can become small and the key observables in our method, the ratios of seismic amplitude to surface pressure change, become difficult to measure accurately.

Citation
Tanimoto, T., & Wang, J. (2020). Shallow Elasticity Structure from Colocated Pressure and Seismic Stations in the Pinyon Flat Observatory and Estimation of Vs30. JGR Solid, (submitted).