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Slip behaviour of the Queen Charlotte plate boundary before and after the 2012, Mw 7.8 Haida Gwaii earthquake : evidence from repeating earthquakes Hayward, Timothy W.


The Queen Charlotte plate boundary, near Haida Gwaii, B.C., includes the dextral, strike-slip, Queen Charlotte Fault (QCF) and the subduction interface between the downgoing Pacific and overriding North American plates. In this dissertation, we present a comprehensive repeating earthquake catalogue that represents an effective slip meter for both faults in the area. The catalogue comprises 730 individual earthquakes (0.3 < Mw < 3.5) arranged into 224 repeating earthquake families on the basis of waveform similarity. We employ and extend existing relationships for repeating earthquake magnitudes and slips to provide cumulative slip histories for the QCF and subduction interface in 6 adjacent zones within the study area between 52.3°N and 53.8°N. We find evidence for creep on both faults; however, the creep rate is significantly less than plate motion rates, which suggests partial locking of both faults. The QCF exhibits the highest degrees of locking south of 52.8°N, which indicates that the seismic hazard for a major strike-slip earthquake is highest in the southern part of the study area. The October 28, 2012, Mw 7.8 Haida Gwaii thrust earthquake occurred in our study area and had a significant effect on the plate boundary. The QCF is observed to undergo accelerated, right-lateral slip for 1-2 months following the earthquake. The subduction interface exhibits afterslip thrust motion that persists for the duration of the study period (i.e., 3 years and 2 months after the Haida Gwaii earthquake). Afterslip is greatest on the periphery of the main rupture zone of the Haida Gwaii event.

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