Shallow S-wave structure at a deep drilling site in Chungnam National University, South Korea with tests for optimal array shapes for f-k analysis and applications of Bayesian inversion method

Abstract:

Microarray is a useful tool to reveal shallow subsurface properties at specific sites with high resolution. In particular, the way using passive sources (i.e., ambient seismic noise) are highly cost-effective and convenient. In this study, six different deployments of geophone arrays were tested with two different gains of sensors (6 and 36 dB), to estimate shear-wave velocity structure at a deep drilling site in Chungnam National University, South Korea. The obtained data were processed using the frequency-wavenumber method to derive Rayleigh wave phase velocity dispersion curves. We used a hierarchical Bayesian inversion method to obtain an average shear-wave velocity profile. Measured dispersion data were generally consistent in the frequency range of 2-6 Hz, not much depending on the shape of arrays. However, arrays with maximum inter-station distances below 60 m showed biased measurements around 4Hz. Dispersion curves from tests with the 6dB gain were not reliable at low frequencies (<2 Hz).