Near-surface shear-wave velocity structure of the Chiayi area, Taiwan

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 (f-k) 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.