Seismotectonics of Canada's West Coast

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Seismically active faults associated with plate tectonic processes endanger almost 3M people and societal infrastructure along Canada's west coast. They include "megathrust" plate boundaries offshore Vancouver Island and Haida Gwaii as well as smaller scale but comparably hazardous structures within the North American and Juan de Fuca plates in closer proximity to population centers like Vancouver and Victoria. The proposed research program improves our understanding of these structures (and so our ability to mitigate their associated hazards) through A) application of state-of-the-art automatic earthquake detection algorithms to publicly accessible seismic waveform archives, B) simultaneous recovery of Earth's velocity structure and precise earthquake relocation, and C) automation and application of a novel algorithm that we recently developed for quantifying fault parameters and the stress regime of small earthquakes. Preliminary analyses demonstrate that approximately 3 times as many earthquakes as currently exist in the Geological Survey of Canada catalogue can be detected using non-specific automatic detection algorithms, and that a factor of 10 times as many earthquakes as currently catalogued can be identified when template matching algorithms that search for waveforms similar to known events are subsequently employed. These algorithms supply accurate arrival-times, amplitudes and polarities of waveforms that will be used in two subsequent stages of analysis. First, high-precision relative arrival-times permit the resolution of detailed subsurface geology and its relation to seismogenic structures using double-difference tomography, enabling insights into dynamic processes responsible for earthquakes in different tectonic environments. Second, recent advances in moment tensor inversion by our group harness waveform amplitudes and polarities of small earthquakes. An earthquake moment tensor is a point-source representation of fault geometry and slip. The availability of multiple independent moment tensors for a given area enables calculation of the regional stress field and therefore seismic risk assessment. Since small earthquakes overwhelmingly dominate catalogues, our approach will allow detailed analysis of fine-scale, spatio-temporal variations in the stress regime characterizing the wide range of tectonic environments represented in western British Columbia. In particular, regionally targeted studies undertaken by diverse HQP will investigate the plate boundaries offshore Vancouver Isand and Haida Gwaii, crustal faults on Vancouver Island, the Nootka Fault Zone, the Queen Charlotte triple junction region, and the Coast Shear zone. Results from this program will lead to significant impacts in  a) assessment of seismic hazard, b) understanding of the physical processes leading to seismogenesis, and c) description of lithospheric structures and evolution, along Canada's west coast.