A new 500-m gridded digital bathymetric data set has been produced by compiling available shipboard bathymetric data supplemented by global bathymetric data sets in the area between 18°N and 27°N, and from 117°E to 125°E. Combined with topographic data from GTOPO30, a global land data set in 30 are-second grid spacing, this new digital elevation 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 arc-minute is retained. This DEM provides the best topographic information at present on a regional scale, which helps to reveal many of the morphotectonic 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 the region are presented. The Taiwan Strait is characterized by low relief sea floor with two NE-SW trending depressions and a shallow bank in the center of the strait. Submarine canyons mark the continental slope. In the area off southern Taiwan, N-S trending ridges and troughs are the major morphological features, however, several NE-SW trending lineaments have been identified in the Luzon forearc region. Off eastern Taiwan, submarine canyons and topographic features related to sedimentary processes along the eastern flank of the Luzon Arc are revealed in detail. A prominent N-S t trending linear ridge, the Gagua Ridge, located along 123°E on the West Philippine Basin floor is entering the Ryukyu Trench and has produced a big re-entrant at the frontal portion of the Yaeayma Ridge. EW to NW-SE trending linear shear zones are observed over the Yaeyama Ridge. These linear faults are the results of westward migration of the frontal portion of the accretionary wedge due to oblique convergence. A series of four forearc basins have been identified. Different depths of the forearc basins reflect lateral variation of the forearc region from oblique subduction to collision. Along the northern wall of the Southern Okinawa Trough, faulted slope and subsided shelf blocks suggest that this region is under post-collisional extension, and the active extension of the Southern Okinawa Trough is advancing westward toward Taiwan.