Submarine mass movements on the northern margin of the southern Okinawa Trough, offshore NE Taiwan

The southern Okinawa Trough back-arc basin has extended in the East China Sea continental margin where large volume of sediments on the seafloor is accumulated. The northern continental slope of the southern Okinawa Trough offshore Taiwan has been cut across by three major NW-SE trending submarine canyons. In order to understand the morphologic seafloor patterns of submarine mass movements on both sides of the Mienha Canyon, we have collected multi-channel seismic (MCS) reflection, subbottom profiler and multi-beam swath data during OR1-1387 and OR2-1573 cruises. In the west side of the Mienha Canyon, numerous small gullies are developed in the upslope areas where water depths are shallower than about 300 m. It is generally reflects an active erosion environment. Steep scarps and parallel channel systems are well developed in the slope of water depths between 300 to 800 m. In the downslope area where water depths are greater than about 800 m, submarine mass landslide with chaotic facie was found. In contrast, gentle bathymetric features and well-developed canyons are observed in the east side of the Mienha Canyon. Sub- bottom profiler shows that submarine mass transport and deposit in water depths greater than about 350 m. Several disturbed unconformities and seamounts were found in MCS profiles. Therefore, the features in the east side of the Mienha Canyon may suggest that submarine mass movements had well developed through several times. In contrast, the tectonic context in the west side of the Mienha Canyon could be unstable and may generate large mass movements in the future.