Seismic and electromagnetic experiments as part of the
Western Churchill NATMAP Program

Alan G Jones(1), Isa Asudeh(1), Greg Clarke(2), Dave Eaton(2), 
Ian Kay(1), Dave Snyder(1) and Don White(1)

1: Geological Survey of Canada
   615 Booth Street
   Ottawa, Ontario, K1A 0E9

2: Department of Earth Sciences
   University of Western Ontario
   London, Ontario, Canada   N6A 5B7

One of the principle objectives of the Western Churchill NATMAP 
Program is investigating the evolution of the late Archean and
Paleoproterozoic lower crust and upper mantle. A 400-km-long N-S 
profile of eight teleseismic and magnetotelluric stations addresses 
this objective by providing a lithospheric geophysical cross-section 
across the Snowbird Tectonic Zone. The stations were located 
equidistantly about Baker Lake, from close to Whale Cove to beyond
Woodburn Lake.

The eight teleseismic stations were operating from early-May until 
late-September, and during that time there was reasonable earthquake 
activity. 
 
Magnetotelluric recordings were accomplished with four
stations operating to the north of Baker Lake from early-July to
early-August, and to the south of Baker Lake from early-August
until late-September. Geomagnetic activity was high during this 
period, requiring care with MT response function estimation due
to the effects of the no-uniform source-field contributions.

Both sets of instrumentation were the fond meeting location of
plastic-chewing animals, resulting in interrupted data acquisition
at four of the teleseismic sites, and total electric field data
loss from one MT site. Protective covering alleviated most of
these problems, but resulted in more innovative investigation 
by the animals.

A very preliminary analysis of the recorded teleseismic data indicates that 12
earthquakes were of sufficient magnitude and at appropriate distances to use
in anisotropy studies.  One event provided SKS splitting observed at
seven stations, each of six other events provide estimates of much lower
quality and at only a few of the stations.  The tentative fast directions
of  observed anisotropy appear to group the stations on either side of Baker
Lake.  The four stations to the south have fast directions trending around
060 degrees; the stations to the north have a spread of fast directions but
generally trend toward the northwest-southeast.  The best-constrained delays
range from 0.8 to 2.45 seconds.

The MT data are testimony to a crust and mantle that is absent of any
major electrical features seen elsewhere in Canada and around the
globe. This implies that there is not an anomalous zone of enhanced
conductivity that can be readily associated with known anomaly
generation. A minor effect at low periods is seen at Baker Lake,
suggestive of a small, mid-crustal anomaly.

Further details will be presented.