| dc.description.abstract | Microtremor measurement has been increasingly adopted to assess site amplification and S-wave velocity profile at sites. However, the composition of microtremor is still a debatable issue. Nakamura claimed that the resonant peak on the dominate frequency of HVSR of microtremor is mainly constructed by the multi-reflection of SH waves rather than Rayleigh waves. This study identified the theory via several evidences: (1) Large disparity on amplifications between ellipticity of Rayleigh waves and HVSR of microtremor; by contrast, disparity between SH transfer function and HVSR of microtremor is much smaller. (2) Phase velocities sometimes become unstable when near the dominate frequency. (3) The difference of particle motions of resonant peak and trough. (4) The ellipticity of Rayleigh waves can not simulate the double peak at a known site, whereas the SH-wave transfer function can. Hereafter, this study developed a joint inversion method to estimate S-wave velocity profiles more accurate and increase the detectable depth until bedrock for a small array. By using the technique, S-wave velocity subsurface structures were estimated at seven strong motion stations in the Taipei Basin. Furthermore, significant discrepancy was detected on each HVSR of TAP089, and then adopted the HVSR inversion to find the 3D subsurface structure beneath this array. Additionally, empirical equations for S-wave velocity in the Ilan area and the Taipei Basin were evaluated by relating the relation of S-wave velocity, N-value, and depth using a multivariable regression approach. Three extrapolations called LSS, STS, and BCV were examined in this study by using 328 DH, and the BCV is obviously the most accurate one. Therefore, a new site classification for TSMIP stations in Taiwan was proposed.
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