Investigation of Velocity Structures on Seismic Stations

Investigation of Velocity Structures on Seismic Stations

The objective of this project is to investigate the velocity structures of shallow and deep soil layers on 18 seismic stations located in Tainan, Kaohsiung, Pingtung and Yilan regions. Two kinds of methods were conducted in this study. One utilized the SASW 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 method used the micro-tremor array methods, wherein natural surface vibrations are recorded by 10 recorders arranged in an array. The frequency-wave number analysis was followed to identify the dispersion curve of soil layers, and the genetic algorithm search method was applied 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 can be obtained by the stress wave propagation method while the velocity structures of deep layers below 10 to 20 meters by the micro-tremor array tests.