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Utilising UAV Lidar to Investigate Potential Late Quaternary Surface Ruptures Along the San Juan Fault on Vancouver Island, BC

Description: 

Identifying active crustal faults within the northern Cascadia forearc is challenging due to low rates of recorded seismicity, late Quaternary glacial scouring, and dense vegetation that often obscures fault-related geomorphology. However, recent research has identified surface ruptures along the Leech River, Beaufort Range, and XEOLXELEK-Elk Lake faults on southern Vancouver Island, which each pose a considerable risk to the >500,000 people that live in this area. We investigate the San Juan Fault (SJF), another putative active fault within this region. The SJF is an 80 km long, E-W striking, terrane-bounding fault, which displays a conspicuous topographic lineament similar to the known-active Leech River fault located ~10 km to the south. Originally a collisional suture between the Wrangellia and Pacific Rim terranes, it is last known to have accommodated left-lateral slip during the Eocene driven by accretion of the outboard Crescent-Siletz terrane. The position of the SJF in the forearc of the active Cascadia subduction, its favourable orientation relative to the regional stress field, and its strong topographic signature have led some to hypothesise that it is seismically active, but no convincing evidence has been found yet. We utilise both airborne lidar and uncrewed aerial vehicle (UAV) lidar to map the surface trace of the SJF. The UAV lidar is capable of collecting much higher density point clouds (2-3X that of conventional airborne lidar) and thus produce sub-meter resolution bare earth models, allowing for identification of fine-scaled features. A scarp-like feature is evident in the lidar data, but it is unclear whether it records Quaternary surface rupture or differential erosion during glaciation, a challenge commonly faced by tectonic geomorphologists working in previously glaciated terrain. We look for evidence of late Quaternary reactivation along the eastern half of the SJF (offsets to glacial landforms and river channels, and scarp morphology) and consider sites where paleoseismic studies could confirm a tectonic origin.

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults - I

Type: Oral

Date: 5/1/2024

Presentation Time: 09:00 AM (local time)

Presenting Author: Guy

Student Presenter: Yes

Invited Presentation: 

Authors