More than 180 regional moment tensor (RMT) solutions for moderate-sized earthquakes (M ≥ 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 (σ1) varies from east–west to north–south to NE–SW from south to north. The stress direction σ1 is consistent with the P axis direction for the largest earthquakes, except in the central and northern Mackenzie Mountains where there is a 16° difference. The Yakutat collision zone shows a steady change in σ1 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 σ1 is oriented ~45° to the strike of the northern section of the fault, which is dominated by strike-slip faulting, and ~60° 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.
The structure and kinematics of the continental intra-arc Taupo Rift have been constrained by fault-trace mapping, a large catalogue of focal mechanisms (N = 202) and fault slip striations. The mean extension direction of~137°is approximately orthogonal to the regional trend of the rift and arc front (α = 84°a nd 79°, respectively) and to the strike of the underlying subducting Pacific Plate. Bending and rollback of the subduction hinge strongly influence the location, orientation, and extension direction of intra-arc rifting in the North Island. In detail, orthogonal rifting (α = 85-90°) transitions northward to oblique rifting (α = 69-71°) across a paleovertical-axis rotation boundary where rift faults, extension directions, and basement fabric rotate by~20-25°. Toward the south, extension is orthogonal to normal faults which are parallel to, and reactivate, steeply dipping basement fabric. Basement reactivation facilitates strain partitioning with a portion of margin-parallel motion in the overriding plate mainly accommodated east of the rift by strike-slip faults in the North Island Fault System (NIFS). Toward the north where the rift and NIFS intersect,~4 mm/yr strike slip is transferred into the rift with net oblique extension accommodating a component of margin-parallel motion. The trend and kinematics of the Taupo Rift are comparable to late Miocene-Pliocene intra-arc rifting in the Taranaki Basin, indicating that the northeast strike of the subducting plate and the southeast extension direction have been uniform since at least 4 Ma.
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