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Change in slide direction of submarine landslides in the Pliocene‐Quaternary deposits near the Shimokita Peninsula, northeast Japan, using 3D seismic data

Submarine landslides constitute a major mass transport process from shallow‐ to deep‐sea and may have catastrophic impacts on both offshore infrastructure and coastal areas. Previous studies on submarine landslides have focused on triggering mechanisms and precondition perspectives, targeting limited numbers of short‐term landslide events. Consequently, few studies have addressed long‐term changes in landslide characteristics, including volume, direction, and timing. The areas studied herein are located on the continental slope facing the Japan Trench off the Shimokita Peninsula, northeast Japan, where a number of large‐scale translational‐type submarine landslide and accompanying unique dike structures have been identified in Pliocene to Recent deposits via 3D seismic data analysis. Here we developed a procedure for recognizing landslide deposits in 3D seismic data from the survey area, then investigated the 3D deposit distributions in detail. Because translational landslides preserve original structures, they can be used to estimate landslide volume. Parallel dike swarm features, which are interpreted as dewatering paths formed soon after landslide events, enable estimation of slide direction in time‐slice images. Such analysis also allows differentiation of landslide deposits from background sediments and estimation of landslide volume. Landslides exceeding 50 km3 in volume have occurred numerous times in the past 6 my. Landslides directions are observed from southwest to northeast over this entire period, whereas slides trending northwest to southeast started at ~ 2 Ma. Although the landslide sizes vary greatly, the average landslide volumes are roughly constant throughout Pliocene and Quaternary time. Such shifts in long‐term trends suggest a change in tectonics in the landslide source region. These unique long‐term records (over 6 my) are enabled by the specific conditions in the study region, which include translational landslides, parallel dike swarms, and monotonous lithology.