Investigation of Velocity Structures of Seismic Stations: Changhwa and Yunlin Region

Investigation of Velocity Structures of Seismic Stations: Changhwa and Yunlin Region

The objective of this project is to investigate the velocity structures of shallow and deep soil layers of 27 seismic stations in Changhua and Yunlin region. Two kinds of methods were considered in this study. One used the stress wave propagation methods combining the SASW method and the impulse response method to obtain the S-wave velocity structure of shallow soil layers by applying a mechanical source. The stress wave propagation theory and the forward iteration process were used to determine the wave velocities and thickness of shallow layers. The other used the micro-tremor array methods, which natural surface vibrations are recorded by 10 recorders arranged in an array. The frequency-wave number analysis is used to identify the dispersion curve of soil layers, and the genetic algorithm search method is used to obtain velocity structures of deep layers by an inversion process. The results from the field tests showed that the wave velocity structure of shallow layers within 10 to 20 meters could be obtained by the stress wave propagation method, and the velocity structures of deep layers below 10 to 20 meters could be obtained by the micro-tremor array tests.