Submarine landslides at subduction margins: Insights from physical models

Submarine landslides, which commonly develop along subduction margins at the front of accretionary prisms, have recently been recognized as one of the most serious geohazards. To investigate the mechanical processes involved in the development of these landslides, a series of sandbox experiments were performed, and the results were analyzed using the digital image correlation (DIC) technique. Numerous slope failures, which may be analogous to natural submarine landslides, were produced on the model surface. The slope failures can be classified as follows: Type I failures, which are relatively small but are frequently developed on the lower parts of the slope; and Type II failures, which are relatively large and cover the entire slope, but occur less frequently. Detailed observations reveal that the failure process can be divided into four stages: 1) pre-failure, 2) steepening of the lower slope, 3) Type I failure, and 4) Type II failure. The minor Type I slides act as precursors of major Type II failures. Each slope failure produces a topographic undulation, triggering events in adjacent areas and a lateral migration of discrete slope failures. Although such experiments provide useful insight into slope failure processes, a detailed 3D analysis of the failed sediment is vital if we are to understand the precise history of thrust activity at subduction margins. Recent and Miocene accretionary prisms along the Nankai Trough, Japan, display the geometric and lithologic characteristics of Type I and Type II failures in their slide deposits.