Southwestern Yukon is a seismically active zone of crustal deformation including multiple large, dextral strike-slip fault systems with overlapping activity. In this study, we perform double-difference relocation to the USGS earthquake catalogue for this region to produce a relocated catalogue of 5536 seismic events above magnitude 1.5 from 2010–2021. The relocated catalogue demonstrates better spatial resolution of linear features and the removal of grid location artifacts in depth. The relocated catalogue has smaller travel time residuals and smaller residual standard deviations showing that the new catalogue has improved absolute locations. From bootstrapping, we estimate the location uncertainties for the relocated events to be on the order of 1.2–2.4 km in the horizontal direction and 1.5–2.1 km in the vertical direction. From the relocated events, we interpret new faults including a fault connecting the Totschunda and Denali faults, a connector fault between the Totschunda-Duke River fault system and the Fairweather fault, and multiple smaller faults connecting the Fairweather and Denali faults. The significantly reduced uncertainty in depth also permits constraining the seismicity predominantly to the uppermost 10 km of the crust.

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.

The 2008 Wells, Nevada Earthquake Sequence: Source Constraints using Calibrated Multiple Event Relocation and InSAR

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.

The following report describes the settings, causes and geological controls of landslides in the Alaska Highway corridor. Although diverse geologic, geomorphic and climatic environments exist in the region, most landslides are related to the presence of shallow bedrock or permafrost, unconsolidated sediment on steep slopes, weak bedrock, groundwater hydrology, river erosion or the degradation of ice-rich permafrost. Where geologic controls provide appropriate settings, intense rainfall, rapid snow melt and seismic events play important roles in triggering failures. Rainstorms that reach thresholds of combined intensity and duration have triggered abundant shallow landslides within the corridor. Debris flows have historically posed the highest risk to lowlying regions and are capable of damaging settlements and transportation routes. The Shakwak Valley has the highest concentration of landslides within the corridor due to the abundance of steep slopes, high relief and widespread discontinuous permafrost. In Wellesley Depression, shallow permafrost and its subsidence has an important influence on slope instabilities. Landslides in the Yukon Plateau primarily relate to the presence of silt- and ice-rich tills on steep valley sides as well as the incision of fine-grained lacustrine terraces in valley bottoms. Debris flows after intense rainfall events are the most common form of landslide in the Kaska Mountains. Finally, in Liard Lowland, failures associated with glacial meltwater and modern stream incision are the most common landslide events. Permafrost plays an important role in landslide processes in the corridor due to its influence on soil moisture, drainage and strength. Slopes composed of icy sediment that have been burned by forest fires are particularly vulnerable to rapid mass movements due to permafrost degradation. The consequences of the dramatic increase in landslide potential after fire should be considered in local fire management plans. The climate¿s local and regional influence on hydrology, fire frequency and permafrost distribution greatly affects landslide processes. Current climate change projections call for warmer temperatures and increased precipitation for the Yukon in the next half century. Among the anticipated effects of global warming in southern Yukon, increased incidents of intense snowmelt and/or precipitation events, river migration, permafrost degradation or forest fires may lead to an increase in landslide frequency and/or magnitude within the settings described in this report. The most significant impact of increased landslide activity may not be a direct impact. Rather, increased sediment input from landslides will likely increase stream channel instability and flooding. This would be particularly acute in the vicinity of alluvial and colluvial fan complexes along Kluane Lake where highway maintenance is already a challenge.

This contribution focuses on the analysis, characterization, and mineralization control of northeast-southwest oriented, magnetic heterogeneities of the allochthonous to parautochthonous Intermontane terranes of the North American Cordillera of western Yukon and eastern Alaska. Our interpretation of publically available magnetic datasets proposes sixteen zones of linear discontinuities oriented semi-perpendicular to the northwest-southeast Cordilleran deformation front and mid-Cretaceous Dawson Range magmatic arc. These magnetite-destructive corridors are interpreted as steeply dipping, brittle fault zones and fracture arrays of extensional, oblique-extensional, and strike-slip kinematics responsible for localized structural damage. Their spatial correlation with known mid to Late Cretaceous magmatic-hydrothermal mineralization suggests a first-order structural control in eastern Alaska, while a secondary role is interpreted for Yukon’s Dawson Range.

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.

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

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.