Digital elevation model offshore Taiwan and its tectonic implications

A new 500-m gridded digital bathymetric data set has been produced by compi ling available shipboard bathymetric data supplemented by global bathymetri c data sets in the area between 18 degrees N and 27 degrees N, and from 117 degrees E to 125 degrees E. Combined with topographic data from GTOPO30, a global land data set in 30 are-second grid spacing, this new digital eleva tion model (DEM) reveals the regional as well as local morphology of Taiwan and its offshore area. Spatial resolution of 1 km is achieved in the area off eastern and southern Taiwan where swath bathymetric data are available, In other areas where ship tracks are sparse, a spatial resolution of 4 are -minute is retained. This DEM provides the best topographic information at present on a regional scale, which helps to reveal many of the morphotecton ic features related to the active tectonic processes of subduction and are- continent collision in this region. Using 2-D shaded topographic maps and 3-D physiographic diagrams generated from the DEM, the major morphologic features in each tectonic province of t he region are presented. The Taiwan Strait is characterized by low relief s ea floor with two NE-SW trending depressions and a shallow bank in the cent er of the strait, Submarine canyons mark the continental slope. In the area off southern Taiwan, N-S trending ridges and troughs are the major morphol ogical features, however, several NE-SW trending lineaments have been ident ified in the Luzon forearc region. Off eastern Taiwan, submarine canyons an d topographic features related to sedimentary processes along the eastern f lank of the Luzon Are are revealed in detail. A prominent N-S trending line ar ridge, the Gagua Ridge, located along 123 degrees E on the West Philippi ne Basin floor is entering the Ryukyu Trench and has produced a big re-entr ant at the frontal portion of the Yaeyama Ridge. E-W to NW-SE trending line ar shear zones are observed over the Yaeyama Ridge. These linear faults are the results of westward migration of the frontal portion of the accretiona ry wedge due to oblique convergence. A series of four forearc basins have b een identified, Different depths of the forearc basins reflect lateral vari ation of the forearc region from oblique subduction to collision. Along the northern wall of the Southern Okinawa Trough, faulted slope and subsided s helf blocks suggest that this region is under post-collisional extension, a nd the active extension of the Southern Okinawa Trough is advancing westwar d toward Taiwan.