Induced Stresses and Fault Potential In Eastern Canada Due to A Disc Load: A Preliminary Analysis

Abstract

In order to understand the causal relation between postglacial rebound and earthquakes, a simple disc load model is used to: (1) calculate stresses induced in the lithosphere and mantle by glacial loading, melting and postglacial rebound; and (2) evaluate the effect of glacial loading/rebound on the failure potential for earthquakes in the upper crust. the dependence of the failure potential and the actual mode of failure on the coefficient of friction, the ambient tectonic stress magnitude/direction, the stress due to the overlying rocks, and lithospheric thickness are investigated. Prominent features of this paper are the inclusion of: (1) a viscoelastic mantle and thus the migration of stress; and (2) the ambient tectonic stress and overburden stress contributions in the calculation of the total stress field. It is assumed that, throughout the Earth, there are optimally oriented pre-existing virtual faults that are initially close to but not at failure; thus, a time-dependent quantity called dFSM (related to the Coulomb-Mohr failure criterion) can be defined such that a negative value of dFSM would advocate faulting or earthquake activities whereas a positive value of dFSM would promote stability. The results indicate that, under all combinations of tectonic stress magnitude and overburden stress, crustal loading promotes fault stability directly underneath the load. Upon the removal of the load, thrust faulting is predicted within the ice margin if the horizontal stress (Sh) induced by the overburden is greater than or equal to the vertical component (Sv) of the overburden stress (1, where=Sh/Sv). Under this condition, theory predicts that faulting or earthquake activity should have reached a maximum immediately after deglaciation. If the horizontal stress induced by the overburden is less than the vertical component of the overburden stress (>1), then theory predicts fault stability within the ice margin. The theory predicts fault instability both north and south of the ice margin. the mode of failure, however, is completely determined by the value of The trade-off between the tectonic stress magnitude and the overburden stress parameter () is also investigated. It is shown that a larger tectonic stress magnitude can be used to compensate a smaller value of the results of this analysis show that variations in the coefficient of friction, lithospheric thickness and a ductile zone below the upper crust do not significantly affect the above conclusions.