Investigation of Shallow Structure at the Western Front of Taiwan Orogen Applying Nonlinear Search Method

Taiwan is not large in area, but it has a complex geological structure due to intense orogeny. From east to west, Taiwan can be divided into five major geological zones: the Coastal Range, the Central Range, the Hsuehshan Range, the Western Foothills, and the Coastal Plain. The southwestern region of Taiwan primarily comprises the Western Foothills and the Coastal Plain. The Western Foothills belong to the foreland of western Taiwan orogen. During the Oligocene, the rifting of the South China Sea led to the development of several east-west-oriented normal faults. Subsequently, in the late Quaternary, the northwestward compression of the Philippine Sea Plate caused a series of north-south-oriented, fold-thrust fault zones in the Western Foothills, and reactivating the normal faults formed during the extensional period. In recent years, most destructive earthquakes have occurred at the deformation front of the orogenic belt, making the study of the region's structural characteristics an important topic. This research utilizes data from a dense seismic array and employs nonlinear inversion of receiver functions and the double beamforming method to investigate the shallow subsurface structure of the Western Foothills. The goal is to provide a more detailed understanding of the structure, which can improve the precision of earthquake location and deepen our knowledge of the area's tectonics.