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Faculty of Graduate Studies

Lekima Yakuden

  • B.Sc. (McGill University, 2024)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Multiplet Earthquakes in The Explorer Region

School of Earth and Ocean Sciences

Date & location

  • Thursday, June 25, 2026
  • 10:00 A.M.
  • Clearihue Building, Room B017

Examining Committee

Supervisory Committee

  • Dr. Edwin Nissen, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor);
  • Dr. Honn Kao, School of Earth and Ocean Sciences, UVic (Co-Supervisor)
  • Dr. Andrew Schaeffer, School of Earth and Ocean Sciences, UVic (Member)

External Examiner

  • Dr. Jochen Braunmiller, School of Geosciences, University of South Florida

Chair of Oral Examination

  • Dr. Daniela Damian, Department of Computer Science, UVic

Abstract

Multiplet sequences are earthquake sequences that have two or more mainshocks that occur close in time and space (e.g., doublets, triplets), as opposed to a single mainshock as predicted by traditional earthquake models. Multiplets appear to occur disproportionately frequently in the Explorer region off the west coast of Canada. The young oceanic Explorer region forms the triple junction between the North American, Pacific, and Juan de Fuca plates, and is undergoing complex deformation across broad transform zones and ridges between the Cascadia Subduction Zone and Queen Charlotte Fault. We use a combination of earthquake relocation and teleseismic waveform modelling to characterize two multiplet sequences in the Explorer region: a Mw 6.5, 6.4 doublet on the Revere-Dellwood Fault Extension (RDFE) and a Mw 6.5, 6.8, 6.5 triplet in the Sovanco Fracture Zone (SFZ). Relocation drastically improved relative event location accuracy and clarified seismicity patterns hinted at by automated catalogue locations. Centroid moment tensor results confirm the Explorer region's thin seismogenic thickness and allow us to match the mainshocks' kinematics with bathymetric fault scarps. The 2008 doublet sequence triggered remote aftershocks clustered perpendicular to the RDFE under Moresby Channel, ∼30 km to the north of the mainshocks, but did not produce aftershocks on the RDFE itself. We calibrate our event relocations of this sequence using a novel catalogue from the PACSAFE OBS array, and explore earthquake triggering mechanisms to explain the aftershock distribution. Predicted seismicity promotion from static Coulomb stress change is consistent with our aftershock locations, though they do not help us clarify their kinematics or time dependence. The 2018 triplet sequence activated faults along the entirety of the SFZ and its bounding ridges. All three mainshocks occurred in the western SFZ, which was previously thought to be seismically quiescent. Previous studies in the SFZ have exclusively documented large earthquakes occurring on a set of northwest-trending scarps in the southern SFZ, but the third mainshock of this triplet appears to have ruptured the northeast-trending faults in the northern SFZ. Together, these observations motivate a reassessment of regional tectonic models, which are predicated on a lack of seismicity in the western SFZ and uniform earthquake slip directions. We further suggest that the high degree of fault segmentation in the SFZ may play a role in multiplet occurrence, drawing on observations of multiplets in the tectonically similar South Iceland Seismic Zone.

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