Hanging wall deformation of a seismogenic megasplay fault in an accretionary prism: The Nobeoka Thrust in southwestern Japan

During the inter-seismic period, an extensionally stable taper was maintained in the inner wedge of the accretionary prism by dominant vertical loading (σ1), in combination with a lesser amount of horizontal compression (σ2) related to the locking of the mega-thrust. Elastic strain energy in the hanging wall of the inner wedge was co-seismically released by slip on the mega-thrust and horizontal shortening in the outer wedge associated with dynamic ductile weakening of the fault plane. This sudden release of elastic strain caused brittle fracturing with σ1 at a high angle to the shear surface of the Nobeoka Thrust, most of the displacement resulting from deformation of the footwall.