[S03-P] Poster

[S03-P-05] Shallow S-Wave Velocity Structures of the Northern Taichung Area, Taiwan, Using Microtremor Array Data

^○Huey-Chu Huang, Tien-Han Shih, Cheng-Feng Wu (National Chung Cheng University, Chia-Yi, Taiwan)

Shallow S-wave velocities have widely been used for earthquake ground-motion site characterization. We investigate the shallow S-wave velocity structures at the northern Taichung area, Taiwan by using the array records of microtremors at 24 sites. The dispersion curves at these sites are calculated using the F-K method (Capon, 1969); then, their S wave velocity structures are estimated by employing the surface wave inversion technique (Herrmann, 1991). At most sites, the observed phase velocities are almost flat with the phase velocity of about 1000 m/sec in the frequency range from 0.5 to 2 Hz. This suggests that a thickness layer with an S-wave velocity of about 1100~1400 m/sec was deposited. If the S-wave velocity of the Tertiary bedrock is assumed to be 1500 m/sec, the depths of the alluvium at the northern Taichung area are between 270 m and 1400 m. The depth of the alluvium gradually increases from east to west. The S-wave velocity decreases from east to west while the depth is larger than 400 m at the area.