Present-day surface deformation and tectonic insights of the extensional Ilan Plain, NE Taiwan

Taiwan's mountain belt is an ideal location to address major questions regarding mechanisms of lithospheric deformation in convergent settings, mountain building processes from oceanic subduction to continental subduction, and post orogenic extension. In the northeast of this belt, the Ilan Plain is a triangular, deltaic plain characterized by a flat topography close to the sea level, and surrounded by the high mountains of the Hsuehshan Range to the northwest, and the Central Range to the southeast. Its eastern coast faces the western tip of the Okinawa Trough, the back-arc basin of the Ryukyu subduction zone. In this study, we analyzed the present-day surface deformation of the Ilan Plain, aiming at deciphering its relationships with basement faults and the regional geodynamic setting. Our approach is mainly based on surface vertical displacements revealed by Persistent Scatterer Interferometry Synthetic Aperture Radar (PSI), which indicate that there is an area of active subsidence (~18. mm/yr) located in the southern part of the plain in probable connection with active basement faults and in agreement with previous geodetic measurements and existing geophysical data. Our PSI results also suggest that the subsidence occurring in the Ilan Plain has moved from north to south during Quaternary in relation with extrusion of the belt due to the westward propagation of the Okinawa Trough through the Taiwan Mountains.