Stress Diffusion from Plate Boundaries

Abstract

ACCORDING to global tectonics, the outer relatively strong layer of the solid Earth (lithosphere) is divided into seven major and several minor discrete plates separated from each other by the Earth's mobile belts. The mechanism of global tectonics is believed to depend partly or wholly on the application and release of strain energy at mobile belts which lie along plate margins. The isostatic response of the lithosphere to application or removal of a wide surface load such as an icecap is delayed by the viscous response of the underlying asthenosphere to elastic bending of the lithosphere¹. By analogy, the viscous drag of the asthenosphere should also delay the response of the lithospheric plates to relief or application of horizontal boundary stresses on a plate edge, as indicated by an earlier calculation made by Elsasser². We have investigated this using a simple plane two-dimensional model of an elastic plate underlain by a viscous layer. We confirm that the viscous shearing stress of the asthenosphere on the base of the lithosphere is a significant factor in causing stress to diffuse through the lithosphere. We also predict the possible occurrence of a new type of strain wave in the lithosphere, with some resemblance to Voigt waves^3,4.