Seismogenic Structure along the Collision Boundary in the Southeastern Taiwan

Abstract

Longitudinal Valley (LV) is the surface representation of the plate collision and characterized by its narrow and long topographic features. Due to the oblique convergence of the Philippine Sea plate with respect to the Eurasian plate, it is widely considered the collision is in its initial stage in the southern LV and Coastal Range (CR). We explored the lateral variations of the subsurface structure due to the initiation of active collision using 3-D Vp and Vs models and relocated seismicity. High-resolution 3-D Vp and Vs models are determined using data collected by an island wide seismic network and a high-density temporary seismic network. We observe very complex structures with large lateral and vertical variations of seismic property in the study area. Velocity perturbations at shallow depths are largely corresponding to the variations in the surface geology. Velocity anomaly beneath the LV and the CR is characterized by a strong negative anomaly, which may represent the unconsolidated thick sediments observed at the surface. The overall distributions of velocity perturbations at mid-crustal depths (~16 km) are quite different from those observed in the slice views at the shallower depth. A narrow and long linear positive velocity anomaly is noticeable beneath the LV and its southern extension. In the east of the high velocity zone, another linear feature with low velocity pertur