Rejuvenation of submarine canyon associated with ridge subduction, Tenryu Canyon, off Tokai, central Japan

The 130-km-long Tenryu Canyon is an active deep water meandering canyon transversely developed on the tectonically active Tokai (Eastern Nankai) accretionary prism, where the multiple intraplate deformation caused by the arc–arc Izu collision. Over 2000 km of EM 12 data, 3.5-kHz profiles and PASISAR profiles obtained during the KAIKO-TOKAI Project, 1996, IZANAGI data, the bathymetric chart, and the preexisting seismic profile data, enable us to better understand the geomorphology and development of the Tenryu Canyon. The Tenryu Canyon is a very steep entrenched channel with its lower stream steeper in both canyon slope and channel slope. Similarly, the relative height between the channel bottom and the levee surface tends to increase unusually toward the lower reach. A likely interpretation of such geomorphological features is that the Nankai Trough floor, as the termination of the Tenryu Canyon, has subsided, associated with subduction of the Paleo Zenisu ridge. Based on the result of a quantitative analysis, the total amount of relative subsidence of >800 m was estimated in the Nankai Trough floor. As a result, the Tenryu Canyon has rejuvenated, catching up the topographic gap between the subsided Nankai Trough floor and the continental slope.