Structural characteristics of large-scale submarine landslide on a very gentle continental slope off Shimokita Peninsula, Northeast Japan.
Presented by Mr. Yuki NAKAMURA on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session
Submarine landslides have been observed even on very low-angle slope well below the angle of response, and are often greater in size and in migration distance than landslides on land. A number of large-scale submarine landslide (slump) deposits were identified in Pliocene and upper formations by analyzing METI’s 3D seismic data “Sanrikuoki 3D” obtained off Shimokita Peninsula (Morita et al., 2011). The slump deposits generally indicate layer-parallel slip on a very gentle and flat continental slope, and often exhibits imbrication structure formed by repeated thrusting of slide sedimentary sheets and related dewatering structure which occurs in the slip planes and cuts the imbrication vertically. Our research aims to understand modes of submarine landslide occurrence that form in such low-angle continental slope. We have investigated detailed distribution and geometry of the slump deposits, using several seismic data in the survey area, determining a criteria of slip plane, seabed before sliding, top of slump deposit, and slip direction. Slip plane corresponds to the bottom of slid layer. Seabed before sliding is identified as a horizon overlaid by slump deposits at the distal portion of the slumping. The domain between the layer corresponding to slip plane and the seabed before sliding is original thickness of slid sedimentary bed. Top of slump deposits is recognized at a boundary covered by normal layers. Slip direction is determined by imbrication and related parallel dike structure which are both basically perpendicular to the slip direction. Being based on the criteria, we identified slump-dominant horizons and structural characteristics of each slump deposits. The slump deposits are interbedded among normal formation in the Pliocene and Quaternary formations, where each slump deposit is basically composed of the above-mentioned imbrication of thrust sheets and chaotic cover sequence, however, the coherent portion of the imbricated thrust sheets are typically dominant in volume rather than the chaotic portion, avoiding fatal collapse of original sedimentary structure. This may be likely a characteristic feature of slump deposits in such very gentle continental slope. Keywords submarine landslides, slump, low-angle continental slope, Shimokita Peninsula, 3D seismic data