Relocation of earthquakes west of Vancouver Island, British Columbia, 1965–1983

Abstract

In the tectonically complex region of young plate interaction west of Vancouver Island, 360 earthquakes have been relocated. The earthquakes occurred in the years 1965 – 1983, when the Canadian seismograph network in the region did not significantly change configuration, and are in the magnitude range 3–5. A traveltime model was derived and applied to arrival times for a selected, limited set of station–phase combinations. Time corrections for these combinations were derived from joint-hypocentre locations of earthquakes in specific regions using independently located reference events. An algorithm for routine location of offshore earthquakes in this region is suggested.The correlation between seismicity and mapped bathymetrical features is strong along the Revere–Dellwood transform fault and the northern segments of the Explorer ridge – transform fault system. Considerable seismicity occurs inside the Explorer Plate, indicating internal deformation. The Sovanco and Nootka shear zones, the southern borders of the Explorer Plate, are characterized by broad belts of seismicity and evidently are not simple transform margins. The Explorer and northern Juan de Fuca ridges are aseismic in the investigated magnitude range.