Near-Surface Shear-Wave Velocity Structure of the Chiayi Area, Taiwan

Abstract

This paper uses microtremor‐array measurements to obtain an overall view of S ‐wave velocity structure in the Chiayi area, Taiwan. The Rayleigh‐wave dispersion curves are calculated using the frequency‐wavenumber (![Graphic][1] ) spectrum method and then the S ‐wave velocity structure of the area is estimated by surface‐wave inversion. According to the inversion results, the S ‐wave velocities decrease from east to west. If the S ‐wave velocity of the bedrock is assumed to be 1500  m/s, the depths of the alluvium are between 560 and 1400 m gradually increasing from east to west. In order to understand the variations of the shallow S ‐wave velocity in the area, we sketch 2D and 3D maps using the imaging techniques based on interpolation algorithms. From the 3D results, the thickness of the sediments having an S ‐wave velocity in the range 270–1500  m/s increases from east to west; whereas the thickness of the layers having an S ‐wave velocity in the range 1500–2370  m/s decreases from east to west. The results are also in good agreement with the geological and geophysical information of the Chiayi area. Therefore, microtremor‐array measurement provides a good alternate to estimate shallow S ‐wave velocity structure. Online Material: Figures showing observed and calculated phase velocities, f ‐ k spectra, dispersion curves, inverted velocity models, sensitivity kernels, and V S contour maps and electric resistivity maps. [1]: /embed/inline-graphic-1.gif