Basement Imaging Using Sp Converted Phases in Chia-Nan, Taiwan

The Chia-Nan Plain is a long and narrow alluvial plain, located in the west of Central Mountain Range and the east of Taiwan Strait. We used accelerograms recorded from 1992 to 2010 March by the Taiwan Strong Motion Instrumentation Program (TSMIP) stations to study the thickness variations of the Quaternary alluviums beneath the Chia-Nan Plain, the biggest alluvial plain in Taiwan, by examining a Sp converted phase. The thicknesses are estimated by the travel-time difference of S and Sp waves. This technique of using P-S converted phases had a quite success in the previous study of Lan-Yang Plain. By the high seismic activity and dense of TSMIP stations in this study area, we used this technique to depict the variations of Quaternary sediments thicknesses in Chia-Nan Plain. In general, the thicknesses become thicker toward west. Finally, this approach helps us to discuss the shape of Peikang Basement High in the north of Chia-Nan Plain, which plays an important role in the tectonic changing of Taiwan western foothills.