Active deformation of Taiwan from GPS measurements and numerical simulations

Abstract

Using a two‐dimensional distinct element model, we evaluate the relationships between plate kinematics and present‐day deformation in Taiwan where active collision occurs. In particular, the distribution of velocity fields calculated in our models is compared with the actual velocity field revealed by the most recent geodetic data (GPS) obtained in Taiwan and the surrounding islands of the Philippine Sea plate and the Eurasian shelf. The main aim of this paper is to produce a mechanically consistent 2‐D model that accounts for the observed velocity field taken as whole, within the limits of acceptable rheological parameters and reasonable boundary displacement conditions. We evaluate how the active deformation of Taiwan is influenced by the presence of strong and weak zones such as the structural highs in the foreland and subduction zones with accretionary prisms, respectively, major mechanical discontinuities such as the main fault zones in the mountain belt, and the opening of the Okinawa Trough. Particular attention is paid to the role of preexisting discontinuities since the presence of mechanical decoupling along major faults strongly affects the distribution of the velocity and stress patterns. We show that despite parameter uncertainties, several tectonic factors (the presence of the strong Kuanyin and Peikang highs in contrast to the weak subduction zone to the south, the “weak” active regional shear zones, and the opening of the back arc Okinawa Trough) concur to provide an acceptable mechanical model for this regional deformation. These sources are related not only to the geometry of the plate boundary, the direction of plate convergence, and the shape of the Chinese margin but also to the presence of major zones of relative weakness and mechanical decoupling such as the Longitudinal Valley fault zone and the western thrust belt of Taiwan.