Investigation of Velocity Structures of Seismic Stations

The objective of this project is to investigate the velocity structures of shallow and deep soil layers of 18 seismic stations, which have conducted P-S logging tests. 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 many 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 could be obtained by the stress wave propagation method although the P-wave velocity is affected by the water table, and the velocity structures of deep layers could be obtained by the micro-tremor array tests although a lot of measurements and computation time are needed.