ALBERT

Description: 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 study, we present a comprehensive repeating earthquake catalogue that represents an effective slip meter for both structures. The catalogue comprises 712 individual earthquakes (0.3≤ M W ≤3.5) arranged into 224 repeating earthquake families on the basis of waveform similarity and source-separation estimates from coda wave interferometry. 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, creep rates are 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, M W 7.8 Haida Gwaii thrust earthquake occurred in our study area and altered the slip dynamics of 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 (5.7 - 8.4 cm/yr) on the periphery of the main rupture zone of the Haida Gwaii event.