STRESS-INDUCED BY TOPOGRAPHY AND CRUSTAL DENSITY HETEROGENEITIES - IMPLICATION FOR THE SEISMICITY OF SOUTHEASTERN CANADA

The stress induced by the topography and density heterogeneities in the lithosphere has been calculated for a large region covering most of southeastern Canada. The calculations assume that the lithosphere consists of a three-dimensional layered elastic slab overlaying an inviscid fluid. The calculations show that the deviatoric stress difference induced by density heterogeneities and the topographic load is of the same order as the regional tectonic stress (tens of MPa). Stresses appear largest along the Saint Lawrence valley where most of the seismicity is Located (e.g., the Charlevoix and the lower Saint Lawrence areas). The Charlevoix seismic zone was analyzed in greater detail and theoretical focal mechanisms were computed. This analysis shows that the stress induced by surface and internal loading is compressional in this area and the principal stress orientation is consistent with earthquake focal mechanisms and in-situ measurements.