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

Abstract

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.

P and S wave travel time inversions for subducting slab under the island arcs of the northwest Pacific

“…Especially for S waves the resolution is unsatisfactory in many places below 800 km. Laterally, the slab appears to buckle at several locations in the u• mantle, probably due to geometrical convergence similar to that proposed by Minamino and Fujii [1981]. There are apparently three major segmentations of the slab, as shown in horizontal slices in the depth range 400-450 km in Figure 8.…”

Stress due to the interseismic back slip and its relation with the focal mechanisms of earthquakes occurring in the Kuril and northeastern Japan arcs

“…The composite focal mechanism solutions for small earthquakes occurring in the vicinity of the Hidaka belt revealed the same trend (Suzuki et al, 1983a). Several researchers attempted to explain this anomaly as being the effect of change in the strike of the plate margin at the Hokkaido corner (Shimazaki et al, 1978;Kato et al, 1980;Minamino and Fujii, 1981;Hashimoto, 1984). However, it has become evident that these models were too simplistic to explain the stress anomaly in terms of the geometry of the plate boundary.…”

Finite element modeling of deformations of the lithosphere at an arc-arc junction: The Hokkaido corner, Japan.

“…As their model consisted of a thin elastic sheet and boundary tractions, they could not estimate the effects of negative buoyancies. On the other hand, MINAMINO and FUJII (1981) calculated the stresses and displacements for a threedimensional finite element model, but they considered only shear tractions on the interface between the subducted slab and the overriding continental plate. For these reasons, out models may be more realistic than theirs.…”

“…KATO et al (1979) concluded that this anomalous stress may be attributed to the difference in the directions of slip vectors along each of the two trenches. MINAMINO and FUJII (1981) tried to explain this phenomenon by tangential tractions exerted along the interface between the subducted Pacific and the continental plates. However, these studies could not adequately explain the tectonics of the arc-arc junction there.…”