Colloquium: Michael Gurnis

Michael Gurnis, John E. and Hazel S. Smits Professor of Geophysics and Director, Seismological Laboratory, Caltech

Abstract:  Plates are driven by buoyancy forces distributed in the mantle, within cooling oceanic plates (ridge push) and within subducted slabs. Although the case is often made that subducted slabs provide the principle driving force on plate motion, consensus has not been achieved. This is at least partially due to the great difficulty in realistically capturing the role of slabs in observationally constrained models as slabs act to drive and resist plate motions through their high effective viscosity. Slab buoyancy acts directly on the edge of the plate (slab pull), while inducing mantle flow that tends to drag both subducting and overriding plates toward the trench. While plates bend during subduction they undergo a form of ‘plastic failure’ (as evident through faulting, seismicity and reduction of flexural parameters at the outer trench wall).