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TitleEvidence for large Holocene earthquakes along the Denali Fault in southwest Yukon, Canada
AuthorBlais-Stevens, AORCID logo; Clague, J J; Brahney, J; Lipovsky, P; Haeussler, P J; Menounos, B
SourceEnvironmental & Engineering Geoscience vol. 26, no. 1, 2020 p. 1-18
Alt SeriesNatural Resources Canada, Contribution Series 20190100
PublisherGeological Society of America
PublisherAssociation of Environmental and Engineering Geologists
Mediapaper; on-line; digital
File formatpdf
NTS115B/14; 115B/15; 115B/16; 115F/07; 115F/08; 115F/09; 115F/10; 115F/15; 115F/16; 115G/01; 115G/02; 115G/03; 115G/04; 115G/05; 115G/06; 115G/07; 115G/11; 115G/12
AreaKluane Lake; Duke River; Yukon-Alaska Highway; St. Elias Mountains; Shakwak Trench; Crescent Lake
Lat/Long WENS-141.0000 -138.0000 62.0000 60.7500
Subjectssurficial geology/geomorphology; tectonics; paleontology; geochronology; geophysics; stratigraphy; Nature and Environment; Science and Technology; Holocene; earthquakes; earthquake risk; earthquake magnitudes; epicentres; seismic risk; seismicity; bedrock geology; structural features; faults; faults, strike-slip; tectonic history; faulting; crustal movements; displacement; glacial history; glaciation; Wisconsinian glacial stage; landforms; scarps; trenches; deformation; fossils; micropaleontology; microfossils; diatoms; fossil assemblages; biostratigraphy; sediments; lake sediment cores; alluvial fans; outwash; gravels; volcanic detrius; peat; silts; gyttja; clays; sands; glacial deposits; terraces; radiometric dating; radiocarbon dating; geophysical surveys; stratigraphic analyses; stratigraphic correlations; Denali Fault; Wrangellia Terrane; North American Plate; McConnell Glaciation; White River Tephras; lacustrine sediments; glaciofluvial terraced sediments; alluvial sediments; eolian sediments; drones; Phanerozoic; Cenozoic; Quaternary
Illustrationsblock diagrams; location maps; satellite images; tables; geophysical images; photographs; cross-sections, stratigraphic; correlation sections; lithologic sections; profiles; biostratigraphic charts
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2020 01 01
AbstractThe Yukon-Alaska Highway corridor in southern Yukon is subject to geohazards ranging from landslides to floods and earthquakes on faults in the St. Elias Mountains and Shakwak Valley. Here we discuss the late Holocene seismic history of the Denali fault, located at the eastern front of the St. Elias Mountains and one of only a few known seismically active terrestrial faults in Canada. Holocene faulting is indicated by scarps and mounds on late Pleistocene drift and by tectonically deformed Pleistocene and Holocene sediments. Previous work on trenches excavated against the fault scarp near the Duke River reveals paleoseismic sediment disturbance dated to ~300-1,200, 1,200-1,900, and 3,000 years ago. Re-excavation of the trenches indicate a fourth event dated to 6,000 years ago. The trenches are interpreted as a negative flower structure produced by extension of sediments by dextral strike-slip fault movement. Nearby Crescent Lake is ponded against the fault scarp. Sediment cores reveal four abrupt sediment and diatom changes reflecting seismic shaking at ~1,200-1,900, 1,900-5,900, 5,900-6,200, and 6,500-6,800 years ago. At the Duke River, the fault offsets sediments, including two White River tephra layers (~1,900 and 1,200 years old). Late Pleistocene outwash gravel and overlying Holocene aeolian sediments show in cross section a positive flower structure indicative of post-glacial contraction of the sediments by dextral strike-slip movement. Based on the number of events reflecting ~M6, we estimate the average recurrence of large earthquakes on the Yukon part of the Denali fault to be about 1,300 years in the past 6,500-6,800 years.
Summary(Plain Language Summary, not published)
This study shows evidence of paleoseismic activity since the Pleistocene in three different settings along the Alaska highway in Yukon. These are: trenches dug across the Denali fault, sediment cores from a nearby lake and faulting and fracturing in Pleistocene glacial outwash gravels.

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