Stress in Western Canada from regional moment tensor analysis

More than 180 regional moment tensor (RMT) solutions for moderate-sized earthquakes (M> or =4) are used to examine the contemporary stress regime of western Canada and provide valuable information relating to earthquake hazard analysis. The overall regional stress pattern shows mainly NE-SW-oriented P axes for most of western Canada with local variations. In the northern cordillera, the maximum compressive stress direction (sigma 1) varies from east-west to north-south to NE-SW from south to north. The stress direction sigma 1 is consistent with the P axis direction for the largest earthquakes, except in the central and northern Mackenzie Mountains where there is a 16 degrees difference. The Yakutat collision zone shows a steady change in sigma 1 from east-west in the east to north-south in the west. In the Canada-United States border region, RMT solutions suggest a north-south compressional regime may extend through southern British Columbia and northern Washington to the eastern Cordillera. In the Vancouver Island-Puget Sound region, RMT solutions do not show any obvious pattern in faulting style. However, the stress results are consistent with margin-parallel compression in the crust and downdip tension in the subducting slab. Along the Queen Charlotte fault sigma 1 is oriented approximately 60 degrees to the strike of the southern section, which is dominated by high-angle thrust faults. The amount of thrust faulting infers a significant amount of convergence between the Pacific and North America plates in the southern Queen Charlotte Islands region.