Deformation in southeastern Alaska and southwest Yukon is governed by the subduction and translation of the Pacific-Yakutat plates relative to the North American plate in the St. Elias region. Despite notable historical seismicity and major regional faults, studies of the region between the Fairweather and Denali faults are complicated by glacial coverage and the remote setting. In the last decade, significant improvements have been made to the density of regional broadband seismometer networks. We relocate more than 5,000 earthquakes between 2010 and 2021 in the region of southeastern Alaska and southwestern Yukon utilizing these improved seismic networks. With reductions in catalog uncertainty, particularly in depth, we quantify the thickness of the seismogenic layer in the crust throughout the region and locate seismicity on a shallow network of upper-crustal faults. Relocated earthquakes, combined with an updated focal-mechanism catalog, permit estimating and classifying motion of active faults. This includes mapping the Totschunda-Fairweather “Connector” fault, which plays an important role in explaining regional deformation, and identifying new faults like the Kathleen Lake fault. We draw similarities between our seismic observations and simplified conceptual models of regional tectonics, which describe a dominant transpressional regime and localized slip partitioning. Our results support a hypothesis where current deformation is taking place on a well-defined and evolved network of shallow faults in the corridor between the Totschunda-Fairweather “Connector” and Denali faults. https://doi.org/10.1029/2023TC008140

Earthquake source characteristics provide a valuable constraint on fault behaviour, crustal stress, and regional plate tectonics. In southwestern Yukon, a region of complex active tectonics, studies of earthquake sources have historically been limited by sparse seismic network coverage. In this work, we leverage recent improvements in station coverage to estimate focal mechanisms for small and moderate-magnitude (M ≥ 2.0) earthquakes from P-wave first-motion polarity data. We invert these data using a probabilistic method that rigorously quantifies mechanism uncertainties. We present preliminary solutions for 363 events, which improve the spatial coverage of the focal mechanism catalogue for this region. We observe contrasting P-axis orientations for events on either side of the Fairweather fault. For events within southwestern Yukon, the distribution of faulting mechanism types and P-axis orientations are relatively consistent. Our focal mechanism solutions support the existence of an unmapped fault south of the Duke River fault. Finally, our results provide a valuable input for subsequent detailed analysis of crustal stress throughout the region.

We studied earthquakes near Burwash Landing, Yukon. Using data from temporary and permanent seismic stations, we enhanced the understanding of both regional and local earthquakes. The study used deep learning and template matching to effectively detect earthquakes, even from noisy data. Following detection, seismic parameters, earthquake location, and magnitude were estimated and refined. The analysis revealed 103 local earthquakes, with 28 located in an area of geothermal resource potential. Notable small-magnitude earthquakes were observed near Bock’s Creek fault. No earthquakes were observed on the Denali fault during the study period. The existence of active faults strike-parallel to the Denali fault suggests that local permeable structures may exist in the area. Regional observations detected 46 432 regional earthquakes in 13 years, but none along a section of the Denali fault near Burwash Landing, Yukon, which we interpret as a seismic gap.

A copy of this thesis is available at the EMR library – QE195.S748 1994.

This map accompanies paper: Johnston, S.T. and Shives, R.B.K., 1995. Interpretation of an airborne multiparameter geophysical survey of the northern Dawson Range, central Yukon: A progress report. In: Yukon Exploration and Geology, 1994. Exploration and Geological Services Division, Yukon, Indian and Northern Affairs Canada, p. 105-111.

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Increased interest in oil and gas exploration in the Yukon is leading to an increase in the use of seismic exploration as a tool for identifying potential drill sites. Although there are a number of techniques that have been developed over the years to minimize disturbances associated with seismic exploration, in some cases the information that needs to be gathered dictates that a less than environmentally optimal treatment be employed. Seismic line cuts can cause a number of outcomes from significant environmental degradation to lines that are barely a whisper on the landscape. Studies conducted in the Eagle Plains and Peel Plateau areas in 2006 and 2007 have provided significant information on the ecology of recovery of seismic lines in these areas. The results of these studies were presented at the 2007 Oil and Gas Best Management Practices Symposium in Inuvik in October, 2007. The South Eastern region is different ecologically from the Eagle Plains and Peel Plateau region. The lower elevation sites in the South Eastern region are vegetated by substantial forests of white spruce, poplars and birch while the Eagle Plains area is tundra at higher elevation and black spruce / Labrador tea scrub forests at lower elevations. The relation to recovery processes in the North Yukon bears consideration as the general processes of recovery illustrate elements that should be considered when seismic lines are cut. This study builds on the studies completed in 2006 and 2007 and provides information that illustrates the ecological characteristics of seismic line recovery as a tool for the continued development of best management practices and standard operating procedures for oil and gas exploration.

This is a summary of stratigraphic units for Yukon.

Detailed geologic mapping of the Dycer Creek area and to the north at Last Peak has revealed several major findings: i) rocks of the Teslin Zone and Cassiar Platform are documented on both sides of the fault; ii) regional transposition ST (sub 2) fabrics observed on both sides of the fault are correlative with one another; iii) late km-scale F (sub 3) folding resulted in the modification of a near horizontal regional foliation on both sides of the fault into a steeply dipping orientation. In the hope of better constraining the timing of regional ductile D (sub 2) and D (sub 3) deformation, geochronology samples of four plutonic bodies have been collected during the 1995, 1996 and 1997 field seasons. Initial results of the study are promising as U-Pb dating of zircons from the Mendocina Orthogneiss within the Teslin Zone has confirmed a Devonian age, and dating of monazites from the Dycer Creek Stock and Last Peak Granite has bracketed the age of regional F (sub 3) folding between 113 and 98 Ma. These findings suggest that at least part of the regional deformation may be younger than previously proposed. A copy of this thesis is available at the EMR library – QE195 G35 1999. This thesis is available online at https://doi.org/10.22215/etd/1999-04228.