MAPPING FAULTS AND STUDYING VOLCANOES: APPLICATIONS OF DOUBLE-DIFFERENCE RELOCATIONS IN BRITISH COLUMBIA

This paper applies double-difference earthquake relocation techniques to investigate a number of sources of seismicity in British Columbia, the most seismically active region of Canada. Southwest British Columbia is a complex region of deformation located above a bend in the subducting Juan de Fuca plate. The region experiences all forms of seismicity associated with subduction zones: megathrust earthquakes at the subduction interface (up to M ~9), large intra-slab earthquakes (up to M ~7), and events from faults in the overlying crust (up to M ~7.3). Each of these types of earthquakes poses significant hazard to major population centres but particularly the crustal events due to their frequency and proximity to the surface and urban areas. By investigating seismicity patterns and the state of stress, we seek a better understanding of the forces driving earthquake activity, the locations of active structures, and the resulting seismic hazard. We present evidence for new active structures in the region using double difference earthquake relocation. Preliminary results show lineations in areas of clustered seismicity and have significantly reduced uncertainties over routine catalogue locations. The lineations that we identify appear to be ‘hidden’ structures that do not extend to the surface. British Columbia also has a number of volcanic belts, including the Anahim hot spot track, where recent swarms of earthquakes have raised questions regarding renewed volcanic activity. Swarm activity was first detected on October 9, 2007, in the vicinity of the Anahim Volcanic Belt, and may represent the reawakening of this seemingly inactive region. Double-difference relocation is applied to microseismic events to investigate how seismicity progresses with time during the swarm. The importance of station geometry in constraining earthquake depths in volcanic regions is also discussed, as this is critical information for monitoring volcanic activity and assessing associated hazards.