Subsurface indicators of active faulting in the central Strait of Georgia, British Columbia and implications for hazard and risk
| dc.contributor.author | Podhorodeski, Anna A. | |
| dc.contributor.supervisor | Leonard, Lucinda | |
| dc.contributor.supervisor | Schaeffer, Andrew | |
| dc.date.accessioned | 2025-06-12T20:09:37Z | |
| dc.date.available | 2025-06-12T20:09:37Z | |
| dc.date.issued | 2025 | |
| dc.degree.department | School of Earth and Ocean Sciences | |
| dc.degree.level | Master of Science MSc | |
| dc.description.abstract | This thesis investigates whether previously unidentified active faulting occurs beneath the central Strait of Georgia, a region located between Metro Vancouver, Nanaimo, and British Columbia’s Sunshine Coast. It also aims to evaluate the implications of such faulting for seismic and tsunami hazard in southwestern British Columbia. To address these objectives, ~2200 km of seismic reflection data are systematically interpreted to identify and catalogue subsurface evidence of active faulting across the study area. Fault interpretation is based on eight objective criteria: reflection offsets, reflection discontinuities, abrupt lateral changes in seismic unit, reflection truncations, associated folding and deformation, abrupt changes in dip, fault shadow, and fault plane reflections. Some criteria appear highly localized and unlikely to delineate structures, whereas others exhibit consistency and lateral continuity across multiple seismic reflection profiles and along linear trends. This analysis enables the delineation of the Central Salish Sea fault zone (CSSFZ; referred to previously as the Fraser Delta fault) beyond its previously mapped surface expression to a length of 12 km, with a possible extension up to 25 km. Subsurface evidence of active faulting is also present beneath a seafloor scarp offshore Bowen Island and a seafloor lineament near Gabriola Island. Given the CSSFZ’s proximity to densely populated areas of British Columbia, deterministic seismic hazard and risk modelling is conducted herein for various rupture scenarios. The CSSFZ’s main strand is modelled with an average dip of ~75 degrees southwest and strike of ~123 degrees. Based on the fault's strike relative to the orientation of local maximum horizontal compressive stress (SHmax), the fault is presumed to accommodate oblique right-lateral slip with a reverse component, although scenarios ranging from pure right-lateral to pure reverse slip are considered. The most impactful modelled scenario – a magnitude 6.7 daytime oblique or reverse rupture – is projected to result in 1,300 deaths, 5,600 uninhabitable buildings, and $18.5 billion CAD (2019) in economic losses across southwest British Columbia due to ground shaking and building damage alone. These hazard and risk results establish a baseline assessment for a fault rupture offshore of Metro Vancouver; secondary hazards (e.g., aftershocks, liquefaction, fires, slope failures) and damage to critical infrastructure could result in further damage and casualties. In addition, the proximity of the CSSFZ to the Fraser River delta, an area prone to submarine slope failure, along with its potential for right-lateral oblique slip, suggests that a rupture may be tsunamigenic. Empirical relations indicate that seafloor displacement during a magnitude 6.7 rupture could generate damaging tsunami runups, with potential impacts for several coastal communities around the central Strait of Georgia. The results in this thesis have demonstrated hazard and risk implications for southwest British Columbia. It is therefore recommended that the CSSFZ be incorporated into future seismic and tsunami hazard and risk assessments. | |
| dc.description.embargo | 2026-05-21 | |
| dc.description.scholarlevel | Graduate | |
| dc.identifier.uri | https://hdl.handle.net/1828/22380 | |
| dc.language | English | eng |
| dc.language.iso | en | |
| dc.rights | Available to the World Wide Web | |
| dc.subject | Strait of Georgia | |
| dc.subject | Salish Sea | |
| dc.subject | Seismic reflection | |
| dc.subject | Seismic hazard | |
| dc.subject | Seismic risk | |
| dc.subject | Faulting | |
| dc.subject | Active tectonics | |
| dc.title | Subsurface indicators of active faulting in the central Strait of Georgia, British Columbia and implications for hazard and risk | |
| dc.type | Thesis |