Quaternary transfer faulting in the Taiwan Foothills: Evidence from a multisource approach

The major structures of the Western Foothills of Taiwan mainly consist of NNE-SSW-trending folds and imbricated west-vergent thrust systems. The additional occurrence of N140 degrees E-striking oblique structures was revealed through a multisource approach involving a Digital Elevation Model (DEM), a study of drainage network anomalies, aerial photographs, Side-Looking Airborne Radar (SLAR) images and SPOT-P and Landsat images. These structures are described from north to south based on new field analyses (including stratigraphy and tectonics studies). They are also compared to seismic data and geodetic reconstruction, in order to evaluate their present-day activity. These N140 degrees E major morphostructures are interpreted as left-lateral transfer fault zones, either inherited from the Eurasian passive margin and/or newly formed in the cover in response to the presence of basement highs within the foreland basin (Peikang and Kuanyin highs). The Sanyi and the Chishan transfer fault zones display a high seismic activity; the distribution of earthquakes and the related focal mechanisms confirm the left-lateral movement along N140 degrees E directions. The Chiayi, Chishan, and Fengshan fault zones act presently as transfer fault zones, as indicated by GPS data. The associated N70 degrees E- to N100 degrees E-trending faults result from the reactivation of normal faults of the Eurasian passive margin as right-lateral strike-slip faults in the Foothills during the Plio-Quaternary collision in Taiwan. We conclude that multisource and multiscale geomorphic studies combined with tectonic analysis in the field yield a significant contribution to the understanding of the structural and kinematic development of the Western Foothills at the front of the Taiwan collision belt.