Active deformation of Taiwan from GPS measurements and numerical simulations

Using a two-dimensional distinct element model, we evaluate the relationshi ps between plate kinematics and present-day deformation in Taiwan where act ive collision occurs. In particular, the distribution of velocity fields ca lculated in our models is compared with the actual velocity field revealed by the most recent geodetic data (GPS) obtained in Taiwan and the surroundi ng 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 accoun ts for the observed velocity field taken as whole, within the limits of acc eptable rheological parameters and reasonable boundary displacement conditi ons. 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 forel and and subduction zones with accretionary prisms, respectively, major mech anical discontinuities such as the main fault zones in the mountain belt, a nd the opening of the Okinawa Trough. Particular attention is paid to the r ole of preexisting discontinuities since the presence of mechanical decoupl ing along major faults strongly affects the distribution of the velocity an d stress patterns. We show that despite parameter uncertainties, several te ctonic factors (the presence of the strong Kuanyin and Peikang highs in con trast to the weak subduction zone to the south, the "weak" active regional shear zones, and the opening of the back are Okinawa Trough) concur to prov ide an acceptable mechanical model for this regional deformation. These sou rces are related not only to the geometry of the plate boundary, the direct ion of plate convergence, and the shape of the Chinese margin but also to t he presence of major zones of relative weakness and mechanical decoupling s uch as the Longitudinal Valley fault zone and the western thrust belt of Ta iwan.