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 (forumla) 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, fk spectra, dispersion curves, inverted velocity models, sensitivity kernels, and VS contour maps and electric resistivity maps.

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