EVIDENCE FOR A ROLE OF THE DOWNGOING SLAB IN EARTHQUAKE SLIP PARTITIONING AT OBLIQUE SUBDUCTION ZONES

A new model, incorporating shear deformation within a subducting slab, is proposed to explain slip partitioning for oblique plate motion at subduction zones. On the basis of investigation of 450 interplate earthquakes at 24 subduction zone segments are find that the degree of slip partitioning is largely correlated with the calculated slab pull force. Such correlation suggests that other than the upper plate deformation, the slab pull force plays an important role in controlling oblique subduction. Our model proposes that the force balance between the slab pull force, the interplate coupling resistance, and the viscous mantle drag (the latter two are passive forces to the former one) produces a lateral shear within the slab, which causes the slab to deform and change its motion direction gradually toward trench normal as it subducts. The amount of direction change, which would be observed as the slip partitioning during earthquakes, therefore is closely related to the major plate driving force at the subduction zone, which is the slab pull force in our model.