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PACIFIC GEOSCIENCE CENTREEARTH PHYSICS BRANCHDEPARTMENT OF ENERGY, MINES AND RESOURCES, VICTORIA, BC Canada V8X 3X3
DIVISION OF SEISMOLOGY AND GEOTHERMAL STUDIESEARTH PHYSICS BRANCHDEPARTMENT OF ENERGY, MINES AND RESOURCES, OTTAWA, ONT Canada K1A 0Y3
Abstract
Available near- and far-field data have been used to reassess and reevaluate the focal parameters of the June 23, 1946 British Columbia earthquake. The preferred epicenter (49.76°N, 125.34°W) is located on Vancouver Island, inland from the population centers along the east coast. This location is consistent with observed intensities, water disturbances, and calculated ground deformation. The hypocentral depth is near 30 km, making surface rupture a distinct possibility. A revised fault-plane solution indicating strike-slip faulting (probably right lateral on a northwest striking plane) though not a unique interpretation, is the most consistent with observed intensities, water disturbances, and calculated ground deformation. A new surface-wave magnitude calculation of 7.2 ± 0.1 agrees with the previously published value of 7.3. Calculated source parameters are as follows: seismic energy release of 5.6 x 1022 ergs; seismic moment of 2.5 x 1027 dyne-cm for the preferred (strike-slip) solution; an apparent stress of 10 bars for the preferred solution. The lack and relatively small size of aftershocks may be indicative of a high stress drop but a reliable evaluation of stress drop is not possible because of uncertainties in estimates of fault dimensions. The epicentral location favors an intraplate setting because it is away from the continental-oceanic boundary and appears to lie within the continental crust of Vancouver Island, which overlies subducted oceanic lithosphere. However, tectonic forces causing the earthquake probably result from the interplate dynamics of the subduction zone.
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