Topographical and Geological Study on submarine canyons off the Pacific Coast in the Japanese Islands

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Submarine canyons around the Japanese islands are divided into 66 submarine canyon systems. I have studied twentyone systems of them which distributed off the Pacific coast of Japan from the topographycal and geological view points. The submarine canyons off NE Japan appears to be chiefly the result of subbottom erosion by some submarine gravity flows.e.g.subaqueous debris flows, turbidity currents and others. The submarine canyons off SW Japan and Hokkaido are resequent canyons. Their plan views vary in sytem patte and trend of canyon axis depending on the offset of faults, trend of fold axis and the other geological structures. There are some differences in plan view and formational mechanism of canyons among those regions, however, the longitudinal topographic sections along canyon axis show a charactcteristic common to all the canyons. Those londitudinal sections divided into two gentle slopes (slope A1 : 0.005-0.006, slope A2 : 0.010-0.018) and two steep slopes (slope B1 : 0.030-0.036, slope B2 : 0.064-0.106) as topographic units. The slope A1 and A2 are equivalent to the upper continental slope off NE Japan and the forearc basins in SW Japan, the slope B1 and B2 are equivalent to the lower continental slope off NE Japan and the continental slopes of SW Japan. All the actual longitudinal sections can be approximated in assemblage of these topographic units. The other results are the discovery of the Shio-no-misaki deep sea fan and a drawing up the detailed chart of canyon systems in the Boso-Sagami canyon systems.