Ian J. Ferguson

POLARIS. POLARIS (Portable Arrays for Lithospheric Analysis and Research Investigating Seismicity) is a national geophysical project,  funded by the Canadian Foundation for Innovation involving scientists from universities in a number of provinces in Canada and two divisions of the GSC. The project involves the establishment of four geophysical arrays: three 30-instrument teleseismic arrays and an array of 30 MT instruments. Initial deployments of the arrays were in southern Ontario to study crustal structure and seismicity in Canada’s economic core, in the Slave craton to study lithospheric structure, and in BC to study crustal structure and seismicity. The MT array has been used for studies of lithospheric structure and aspects related to the induction of geomagnetic signals on powerline and pipleine infrastructure. I have coordinated MT studies in Manitoba, and regional lithopsheric studies in Ontario, and collaborated with C. Samson (Carleton University) on smaller-scale Ontario studies and Slave studies.

In the regional Ontario studies I have acquired MT soundings at 47 sites within the Proterozoic Grenville Province in southern Ontario and installed three observatory MT sites in this region. The MT data consist of long-period (LMT) soundings at 21 sites and broad-band (BBMT) soundings at 30 sites. Initial MT analysis has focused on strike and dimensionality determination. Raw geoelectric strike azimuths correlate with upper crustal geometry. Distortion and variogram analyses suggest the dominance of 2-D structures with galvanic-distortion corrected strikes that have a more east-west azimuth. Partial correlation of MT strike and shear-wave splitting fast directions suggests a component of the seismic anisotropy is related to lithospheric structure. Ongoing analysis involves interpretation of MT data along three north-south profiles, two of which extend profiles from the LITHOPROBE Abitibi Grenville transect. Results show the responses observed near the Grenville Front that have been interpreted by Ji et al. (1996) in terms of shearing in the mantle are restricted to a 100 km wide zone. Also, crust of the Central Metasedimentary Belt has enhanced electrical conductivity relative to the Central Gneiss Belt.

The MT data set was used to select three sites with low noise and low to moderate distortion levels for observatory (long-duration, telemetered) MT recordings. The sites were also chosen so as to extend over a large east-west and north-south part of the Grenville Province The observatory MT sites, which are located at POLARIS seismograph sites, were installed in Summer 2006 and telemetry started in Fall 2006. The 8 Hz five-channel MT data from the observatory sites are telemetered to the GSC in Ottawa using the POLARIS VSAT system and made publicly available on the internet at the POLARIS MT site.

2. Geomagnetically Induced Currents (GICs): Modelling of geomagnetically induced currents (GICs) requires knowledge of the spatial and temporal form of geomagnetic sources, information on the earth conductivity structure at crustal and upper mantle depths, and definition of the geometry and grounding of the infrastructure on which the currents are induced.  The long-term objective of my GIC research is to increase knowledge of how earth resistivity structure and spatial structure of geomagnetic sources affect induction of GICs on powerlines and pipelines. The short-term objective is to use MT array studies in Manitoba to refine earth resistivity models and examine the spatial uniformity of geomagnetic sources. I contributed to a collaborative research project between the GSC, hydro utilities, and universities examining induction of GICs on powerlines in Canada. My work included examination of more than 50 MT studies from across Canada in order to define the large-scale conductivity structure. More recently I participated in a survey in the Ottawa River Valley examining the pipe-to-soil potentials on a gas pipeline and in a POLARIS MT survey in southern Manitoba designed to define the geoelectric response in the south of the province.  

3. Geoenvironmental Studies: My students and I have completed geophysical studies of shallow groundwater targets. Most recently we have been involved in studies imaging abandoned gold mine tailings in Nopiming Provincial Park and examining the in-phase response of  EM31 instruments over clay rich soils in southern Manitoba. Over the last decade we have done research into saline contamination of soil and groundwater resulting from oil production in Manitoba and Alberta. Recently, we have compared EM survey results with 150 soil analyses from a dense 3D grid and used ground penetrating radar profiling to image a contaminant plume. In her M.Sc. research V. Maris examined factors controlling shallow groundwater flow in glacio-lacustrine clays during studies of gypsum deposits. She showed that EM methods (TEM, DC resistivity, and low induction number EM systems) resolved topography on an interface between laminated clays containing a basal aquifer and an underlying unit of massive clays. In an associated study she showed that the EM methods defined sub-surface structure of palaeo-iceberg scours. In a larger-scale groundwater study, the time-domain EM (TEM) method was applied to investigate the interface, at 200-500 m depth, between fresh and saline groundwater in granitic rocks of the Precambrian shield. This study, a joint project with Atomic Energy of Canada Limited, showed that TEM could map the interface, as well as shallow sub-horizontal fracture zones, and provided information on the optimal configuration of future surveys. We have also applied EM methods in studies of other near-surface targets. We investigated a palaeokarst-hosted kaolinite deposit, providing new information on the karst surface, delineation of the deposit, and assessment of different methods in this environment. We have also applied EM and GPR in the investigation the winter dens of red-sided garter snakes. The GPR response images voids on bedding planes at 6-8 m depth, between the water table and the depth of winter freezing. Finally, we have examined ground freezing using DC-resistivity and showed that the resistivity of the clays increases on freezing from 10 ohm.m to 1000 ohm.m.

• Editor of Pure and Applied Geophysics (1998-Present)
• Co-chair of IAGA Working Group I-2 Electromagnetic Induction in the Earth
• Member of POLARIS Steering Committee (1999-Present)

Last Updated: 17th September 2009