Conductive structures in southwestern Canada: a regional magnetometer array study

Abstract

An array of 33 three-component recording magnetometers was operated in June and July 1980 in Alberta and British Columbia south of the Edmonton – Prince Rupert highway. This very large array, with its stations dispersed through 550 000 km2 and on average 150 km apart, had limited resolution and was designed to confirm known conductive structures, discover new ones, and locate them sufficiently for suitable placement of further arrays with closer spaced stations and, therefore, higher resolution. Magnetograms and three sets of Fourier transform anomaly maps are presented. They show the general attenuation of the vertical component of variation fields west of the Rocky Mountain Belt known from previous work and generally attributed to a conductive layer in the lower crust or upper mantle. Two prominent local anomalies are shown by variation fields of periods 15–30 min. The first indicates induced currents near Tête Jaune Cache, west of Jasper. The highly conductive structure carrying the induced currents may include wet sediments in the Rocky Mountain Trench and possibly partial melt at depth associated with recent volcanics. The second local anomaly appears to be associated with a crustal conductive structure that strikes northeast–southwest across southern Alberta and crosses the southeast corner of British Columbia into eastern Washington State. This may be associated with a Precambrian rift in the lower crust discovered by Kanasewich and his colleagues using deep crustal seismic reflections some 15 years ago. Both of these anomalies are under further investigation by means of arrays operated in 1981 in locations indicated by the results of the array reported here. The regional westward attenuation of the vertical fields has been quantified by means of single-station transfer functions and artificial event analysis, as developed by Bailey and others, to show the Z response to unit southwest–northeast horizontal field at three periods, along a profile from Squamish, near Vancouver, to Edmonton. These response curves will be used in model studies of the regional conductive structure.

Electrical conductivity structure of the Purcell Anticlinorium in southeast British Columbia and northwest Montana

“…From these facts, we conclude that the observed pervasive high conductivity in the region is due to some form of mineralization (possibly copper sulphide), rather than due to brines or graphite. (6) This investigation confirms the presence of the Rocky Mountain trench conductor that was postulated earlier by Gough et al (1982), Hutton et al (1987), and Gupta and Jones (1990). As shown in Fig.…”

Coincident conductive and reflective middle and lower crust in southern British Columbia

“…A large-scale geomagnetic depth sounding (GDS) magnetometer array study in 1980 (Gough et al 1982) confirmed both the validity of approximating the gross regional structure by a 2-D model and the existence of a zone of anomalously high conductivity beneath much of the Canadian cordillera, named the Canadian Cordilleran Regional (CCR) conductor by Gough (1986a). A large GDS array in the north-western US states, operated as part of the EMSLAB project (EMSLAB 1988;Booker & Chave 1989).…”

Estimating the Geoelectric Field and Electric Power Transmission Line Voltage During a Geomagnetic Storm in Alberta, Canada Using Measured Magnetotelluric Impedance Data: The Influence of Three‐Dimensional Electrical Structures in the Lithosphere

“…The lithosphere was modeled at 1,000 Ωm (Trichtchenko et al, 2019). The second model, shown in Figure 8, was identical to the first, but also included a northeast-southwest trending 1 Ωm conductor to represent the SABC in south-central Alberta between 20 and 30 km depth based on Gough et al (1982), Nieuwenhuis et al (2014) and Wang (2019) (Figure 8). Note, that in both models, ocean bathymetry was included in padding cells with ocean model cells set to 0.3 Ωm.…”