Dislocation model for strain accumulation in a plate collision zone

Abstract

Following a scheme developed for a subduction zone by Savage in 1983, which was successfully applied to a transform plate boundary by Matsu’ura and others in 1986, a dislocation model for a plate collision zone is formulated. The solution consists of a rigid plate motion and a tensile dislocation. In addition to this, a strike-slip dislocation is needed when the collision boundary is not perpendicular to the plate converging direction. Theoretically predicted gradual change in horizontal displacements over the collision zone well explains the results of GPS continuous observation in central Japan where the Eurasian and Okhotsk plates are thought to be colliding. The maximum uplift rate is predicted as 1/π times that of converging velocity, however the observed uplift rate is much smaller than that, although vertical movements observed by GPS network is much less accurate than horizontal movements. A comparison of the theoretical results with the observation suggests relatively thin elastic plates, whose thickness is about 30 km. The obtained dislocation model has a close connection with a horizontal detachment fault. The displacement fields above the advancing and retreating edges of a horizontal rectangular detachment fault are mathematically equivalent to those of collision and rift zones, respectively, and lateral edges to a transform fault boundary. The displacement fields at a colliding and a rifting boundaries are the same except for their signs.