What Drives Plate Motion?

Abstract. Plate motion is a remarkable Earth process that is widely ascribed to two primary driving forces: ridge push and slab pull. With the release of the first- and second-order stress fields in 1989, it was found that the observed stresses are mainly distributed on the uppermost brittle part of the lithosphere. A modeling analysis, however, reveals that the stress produced by ridge push is mainly distributed in the lower part of the lithosphere. Doglioni and Panza recently showed that slab pull was inconsistent with the geometry and kinematics of plate. These findings suggest that other force is possibly responsible for plate motion and the observed stress. Here, we propose that the pressure of deep ocean water against the continental wall exerts enormous force (i.e., ocean-generated force) on the continent. The continent is fixed on top of the lithosphere, this attachment allows the ocean-generated force to laterally transfer to the lithospheric plate. We show that this force may combine the ridge push, collisional, and shearing forces to form force balances for the lithospheric plate; the calculated movements for the South American, African, North American, Eurasian, Australian, and Pacific plates are well consistent with the observed movements in both speed and azimuth, the RMS of the calculated speed against the observed speed for these plates is 0.91, 3.76, 2.77, 2.31, 7.43, and 1.95 mm/yr, respectively.