Shallow Shear-wave Velocity Structures of TSMIP Stations in Taiwan

Shallow Shear-wave Velocity Structures of TSMIP Stations in Taiwan

The high seismicity and major tectonic features of Taiwan result from active collisions. The wide range of alluvium basins amplify and extend incident seismic waves and can result in earthquakes because of the seismic site effect. In this study, the advantages of the evenly distributed strong motion stations and the numerous records in Taiwan were used to apply the Receiver Function(RF) technique to high-frequency acceleration seismograms recorded by Taiwan Strong Motion Instrumentation Program(TSMIP) stations to estimate the shallow shear wave velocity(Vs) structures. In the RF analyses, an average RF of each station was calculated to enhance the converted phases and reduce the inharmonic arrivals. Based on the geological data, the geophysical data, and the Engineering Geology Database for TSMIP(EGDT) drilling data, an initial layer model with variable Vs and thickness, in conjunction with a Genetic Algorithm(GA) search, was used to model RF and estimate the Vs profile of a station. Finally, the one-dimensional shallow Vs profiles of 763 stations were estimated by RF analysis and forward modeled with the GA search. All the results proved that this method is not only effective for teleseismic records but also strong motion records, and can reconstruct the shallow Vs structure of alluvium basins overlaying a hard bedrock. Based on the Vs structures estimated in this study, a shallow velocity model of Taiwan was preliminarily constructed for applications in seismology and earthquake engineering. In addition, the results were compared with the Vs30(average shear-wave velocity of the top thirty meters of ground) of the EGDT to verify the site conditions of TSMIP stations and to provide important site parameters such as engineering bedrock and Z1.0(depth of the velocity horizon where the shear-wave velocity reaches 1.0 km/sec).