The effect of the contorted 'nose' of a subducting slab on the stress field in the continental lithosphere at an arc-arc junction

Abstract

Summary. In the continental lithosphere, the stress field near the junction of two arc-trench systems often shows a different state from the regional trend. By assuming that the drag forces and nose-shaped contortion of the subducting slab control the state of stress in such a region, the vertical displacements and stress distribution in a continental lithosphere with a concave seaward boundary are calculated using a three-dimensional finite element method. It is also assumed that the drag is applied to a depth of about 60 km which is the depth limit of thrust-type earthquakes along the interplate boundary. It is demonstrated that the anomalous stress field resulting from the contorted 'nose' of the subducting slab extends inland some distance from the corner of an arc-arc junction. The area of anomalous stress field is characterized by surface upheavals and a stress regime conductive to strike-slip faulting, though the extent of this area depends on the model parameters. The degree of contortion, i.e. the width of the contorted 'nose' of the subducting slab, remains arbitrary even when appropriate restrictions such as the conservation of surface area and fixed meeting angle and dip angles of the two neighbouring subduction zones are made in symmetrical models. Applying the model to the Hokkaido corner, i.e. the junction of the Kurile and Japan trenches, the anomalous stress field appears in the south-eastem part of Hokkaido and coincides more or less with geophysical observations.