Modelling Crustal Stress in Southern Ontario

Analysis of stress measurement data from the near-surface to crustal depths in southern Ontario show a misalignment between the direction of tectonic loading and the orientation of the major horizontal principal stress. The compressive stress field appears to be oriented subparallel to the major terrane boundaries such as the Grenville Front, the Central Medisedimentary Belt boundary zone and the Composite Arc Belt boundary zone. This suggests that the stress field has been modified by these deep crustal scale fault zones. In order to test this hypothesis, a geomechanical model was constructed using the three-dimensional discontinuum stress analysis code 3DEC. The model consists of a 45 km thick crust of southern Ontario in which the major crustal scale fault zones are represented as discrete faults. Lateral velocity boundary conditions were applied to the sides of the model in the direction of tectonic loading in order to generate the horizontal compressive stress field. Preliminary results show that for low strength (low friction angle and cohesion), fault slip results in the stress field rotating toward the strike of the faults, consistent with the observed direction of misalignment with the tectonic loading direction. Further analysis of the model may be used to provide constraints on the strength of these faults.