Earthquake source characteristics provide a valuable constraint on crustal stress and regional plate tectonics. Earthquake source studies in Yukon and northern British Columbia have been limited by sparse seismic network coverage. In this work, we leverage recent seismic network improvements to estimate focal mechanisms for small- and moderate-magnitude (M > 2.0) earthquakes from P-wave first-motion polarity data. We invert these data within a probabilistic framework to rigorously quantify mechanism uncertainties. Subsequently, probabilistic earthquake focal mechanisms are used as input for inversions for the orientation of principal stress axes, and stress shape ratio, for spatial windows throughout the region. We implement a novel, data-driven approach to propagate focal mechanism uncertainty in stress inversion. Our results improve the spatial coverage of existing earthquake focal mechanisms and enable an orogenic-scale study of crustal stress near the Yakutat–North America collision. Overall, the region is characterized by a transpressive stress regime. Maximum horizontal compressive stress orientations exhibit a pattern orthogonal to the Yakutat collision syntaxis. Stress inversion results also reveal an abrupt change in orientation east-to-west, which we interpret as a change in stress regime across the Fairweather–Connector–Totschunda fault system that is likely related to coupling between the subducting Yakutat slab and North America. This work improves our understanding of potential earthquake hazards in southwestern Yukon and the surrounding 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.

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

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.

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.

Regional mapping of soil stiffness improves understanding of seismic hazard in northern Canada, specifically southwestern Yukon, where local amplification hazards are largely unknown. Ambient vibration (AV) measurements record microtremor seismic noise used to calculate the horizontalto-vertical spectral ratio (HVSR) and identify resonant frequencies at sites. In-situ estimation of fundamental frequency (f0) is used to characterize sites and map local site amplification hazards. Furthermore, AV measurements permit the estimation of surface-wave propagation speeds at different frequencies (i.e., dispersion). Dispersion measurements are used to infer profiles of shear-wave velocity as a function of depth. We present preliminary site characterization using AV measurements from 23 measured sites in Haines Junction, Yukon. The preliminary results suggest a spatial trend of fundamental frequency laterally, where higher frequencies are identified north of Haines Junction and lower f0 values are identified in south-central Haines Junction. We attribute these observations to the proximity to the Dezadeash River basin.

This paper serves as an update to an earlier paper published by the Yukon Geological Survey: New mineral potential mapping methodology for Yukon: case studies from the Beaver River and Dawson regional land use planning areas (Bullen, 2020). Since the release of the earlier paper, a number of the methods have been modified, and new techniques introduced. These are incorporated into this update paper — the reader is referred to the earlier paper for details of the method itself. Mineral potential maps have thus far been completed for the Beaver River watershed, and the Dawson, Teslin, Na-Cho Nyäk Dun, and Ross River regions. There have been significant updates made to the mineral potential mapping method: 1. Modifications to buffer distance and factors (these are an important fuzzy logic (i.e., non-Boolean) component of the mineral potential mapping process) to enhance mapping outcomes. 2. The introduction of an in-house generated, machine learning algorithm (unsupervised, clustering-type) to classify mineral potential in order to remove the potential for human bias. The method replaces the statistical, areas-under-the-curve approach used previously. 3. A new method for delineating anomalous stream sediment data based on the lithological makeup of each watershed basin. The method computes and compares expected assay values to actual assay values, with values exceeding a certain threshold taken as anomalous. The previous method did not take lithology into account, relying on simple percentile methods only, and was considered insufficiently robust. 4. A new method for categorizing mineral potential confidence. Mineral potential maps produced by the Geological Survey contain measures of bedrock mapping confidence to facilitate land use planning. The updated method is significantly more robust than that used previously. 5. Revisions to the map legend to account for the new, machine learning-based mineral potential categorization methodology. 6. Revisions to the map colour scheme to make them colour blind-safe.

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for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.