Along-Strike Migration of Intermittent Submarine Slope Failures at Subduction Margins: Geological Evidence from the Chikura Group, Central Japan

摘要

Ancient submarine slope failures are exposed in the Plio-Pleistoccne trench-slope basin sediments of the Chikura Group. Based on the lateral tracing of a key tephra bed ("HF") and the sedimentology and geological structure at seven exposures of the failure deposit over a total distance of 5 km, we identified at least five discrete failure events and evidence of lateral variation in the age of the failures, younging to the west. The slope failure deposits therefore represent the lateral migration of intermittent submarine slope failures. The initial slope failure was triggered by earthquake-induced liquefaction at about 2 Ma, and subsequently failures propagated northwards perpendicular to the ancient trench axis. The geological evidence for the systematic lateral migration of intermittent submarine slope failures accords with the migration style identified by physical models of failure propagation.