Stress analysis of the Lithosphere

Abstract

Computer programs have been written to perform finite clement calculations with 3-noded elements for the cases of plane strain, plane stress and axisyrmetry and to produce data for these programs. The latter is specifically orientateo towards (geophysical models and includes a facility for quasi-horizontal boundaries. These have been used to investigate the stress field ansociateo with sedimentary basins and continental margins. From those calculations, the preferential formation of normal faults on. and to the continental side of margins, with the subsequent formation of deep sedimentary basins, is explained. Quantitative studies on the diffusion of stresses through mathematical models of the lithosphere and asthenospherc have given time constants of 200,000 years for plates of the size of the Pacific. Simulated failure has been built into this model and leads to the prediction of a 10 yearly failure cycle with energy releases of 10(^27)ergs. The finite element models have been extended cope with dynamic cases and used to calculate the natural frequencies if free vibration of a sedimentary basin. For a Rayleigh type response the fundamental period has been shown to be directly proportional to the derth of the basin. The natural frequencies calculated are of the same order as those measured in surface waves generated by earthquakes and a Fraunhofer absorption effect is suggested.