A Seismic Structure Study in the Kaoping Area, Southwestern Taiwan

Abstract:

The difference between S wave and S-to-P wave conversion (S_p phase) arrival times is enhanced with Rectilinear Motion Detector filtering to describe alluvial-sediment thickness in the Kaohsiung-Pingtung (Kaoping) plains area. A more complete understanding of the underground structures of the Kaoping area is provided and explains why the surrounding regions in Taiwan experience more earthquakes. Data are based on seismic activity recorded by PANDA for the period 1995 to 1997. The difference between S wave and S_p phase arrival times show that the sedimentary layer is thicker along the west and southwest coast. P wave travel time residuals, high frequency attenuation parameters kappa, and quality factor Q_P, Q_Sand coda waves confirm this result. We also determined the orientation of the Chaochou fault using the first motion of P-waves arrivals. To the east of the Chaochou fault, stress trends southeast-northwest, while to the west, it trends northeast-southwest. The change of stress trends East and West of Chaochou fault suggest the presence of a highly fluid accretionary wedge in the Kaoping area. The Chaochou fault forms a seismically active tectonic boundary with uplift of the hanging wall leading to westward tilting of the basement of the Kaoping plains. We demonstrate these features are why there are relatively few earthquakes in the Kaoping area. The presence of a highly fluid accretionary wedge is indicated by a thick alluvial layer in the west and southwest Kaoping coast; the Peikung High acts as the indenter that may allow seismic energy to escape and reduce the number of earthquakes in the region.