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TitlePreliminary evidence of Late Quaternary faulting in the Rocky Mountain Trench from new LiDAR data and field investigations
AuthorFinley, T; Prush, V; Nissen, E; Miller, B; Sethanant, I; Cassidy, JORCID logo; Rowe, C D
SourceAmerican Geophysical Union Fall Meeting 2021, abstracts; T54A-09, 2021 p. 1 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20210335
PublisherAmerican Geophysical Union
MeetingAmerican Geophysical Union Fall Meeting 2021; New Orleans, LA; US; December 13-17, 2021
DocumentWeb site
Mediadigital; on-line
File formathtml; pdf
ProvinceBritish Columbia; Yukon; Alberta
NTS72; 82; 83; 84; 92; 93; 94; 95; 104; 105; 106; 115; 116
AreaAlaska; Canada; United States of America
Lat/Long WENS-145.0000 -110.0000 65.0000 49.0000
Subjectsstructural geology; geophysics; tectonics; surficial geology/geomorphology; Science and Technology; Nature and Environment; Health and Safety; Holocene; Paleogene; Eocene; geophysical surveys; bedrock geology; structural features; trenches; faults, normal; faults, strike-slip; tectonic history; displacement; seismic risk; seismicity; earthquakes; earthquake risk; field relations; geophysical interpretations; landforms; scarps; sediments; sedimentary structures; Canadian Cordillera; Rocky Mountain Trench; Tintina Trench; Infrastructures; Phanerozoic; Cenozoic; Quaternary; Tertiary
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2021 12 01
AbstractThe Rocky Mountain Trench (RMT) is a ~1500 km-long valley that stretches from northern Montana through the eastern Canadian Cordillera of British Columbia (BC) to the Yukon border, where it continues another 1000 km to Alaska as the Tintina Trench. A series of major faults occupy the RMT for much of its length. Faults that define the Southern RMT have accommodated ~5-10 kilometers of normal displacement, while faults along the Northern RMT are thought to have accommodated ~450 km of dextral displacement. Despite the RMT's remarkably linear topographic expression, these faults are generally believed to be Eocene in age, not Holocene. Here we evaluate the neotectonics and seismic hazard of the RMT based on new lidar data, field investigations, and existing geophysical evidence. We undertook a systematic review of the lidar data and found that while young surface ruptures are not pervasive in the RMT, there are several features of possible neotectonic origin, including fault scarps, sackungen, and river channel offsets. We conducted preliminary fieldwork at several of these sites and found evidence of tectonic deformation in Late Quaternary sediments filling the RMT. In some cases, faults cross-cutting these sediments are not associated with continuous scarps on the surface, highlighting a challenge of paleoseismic work in this environment where dynamic post-glacial (post-13 kya) geomorphic processes may have erased the surface expression of Holocene faults. Detailed mapping and geochronology of glacial sediments and their cross-cutting relations will be necessary to confirm the occurrence and age of past earthquakes. Our observations add to existing evidence of neotectonic activity on the RMT: several poorly located historical earthquakes of M 4-6 have occurred in the vicinity of the RMT and may in fact have occurred along it; local seismograph networks have detected small earthquakes along some segments; and geodetic networks - though sparse - indicate a minor strain gradient across the eastern Cordillera, which may be localized on the RMT faults. Collectively, ~135,000 people live along the RMT, and several major highways, freight railways, hydroelectric dams, and oil and gas pipelines lie within or cross the valley. It is therefore critical that further work is carried out to understand the seismic hazard of the RMT.
Summary(Plain Language Summary, not published)
The goal of this research is to search for evidence of faulting along ancient faults in British Columbia, specifically the Rocky Mountain Trench and associated structures. This work utilizes existing geophysical evidence, new lidar data, and field investigations. This study revealed several features of possible earthquake faulting, including scarps, sackungen, and offset river channel offsets. These results will help guide future detailed studies that will contribute to improved assessments of earthquake hazards in this region.

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