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Dynamics of Submarine Landslides in an Active Margin from Particle Size Analysis, 3D Seismic, and Logs IODP Expedition 338, Nankai Trough, offshore Japan

Z. Moore and D. E. Sawyer

Submarine landslides in the Nankai Trough, offshore Japan, are controlled by slope sediment properties and seismic activity. Laser particle grain size analyses document that sediment samples from 0-­194 meters below seafloor from Site C0021, Integrated Ocean Drilling Program (IODP) Expedition 338 consist of 75% silt, 15% clay, and 10% sand. Given the relatively low clay fraction and frequent earthquakes in this region, I hypothesize that landslides that occur in these sediments behave as low-­viscosity, fluidized failures, as opposed to slow-­moving, cohesive blocky failures. I will test this hypothesis in two steps: First I will conduct a detailed 3D seismic and core-­log correlation of mass transport deposits (MTD) to characterize slope geometry and deposit morphology of the historical record of failures. Second, I will calculate a flow factor (Ff) (Ff = ratio of driving force to resistant force) for each MTD as a proxy for the dynamic behavior when failure occurred. Preliminary results from seismic data indicate that MTDs are thick, and blocky, which is in direct contrast to my hypothesis. One potential mechanism to explain this observation is seismic strengthening in which repeated shaking from non-­failure earthquakes progressively dewater and thus strengthen the sediment and increasing slope stability. Then, when a landslide does eventually occur, it behaves as a cohesive, blocky landslide. This research sheds light on the dynamic behavior of underwater mass movements; a historically difficult problem to address as well as a practical obstacle to deepwater operators needing to install subsea infrastructure in earthquake-­prone environments.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013