A low-frequency magnetotelluric study in southern Saskatchewan
Date
1984-08
Authors
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Journal ISSN
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Publisher
ORCID
Type
Degree Level
Masters
Abstract
A low-frequency magnetotelluric sounding survey was
conducted in the Bengough area of southern Saskatchewan
during the fall of 1981. The objectives of this
investigation were twofold: to locate the western edge of
the North American Central Plains conductivity anomaly in
this region, together with its depth, and to compare the
results given by the customary cross-spectral method of
magnetotelluric data processing to those obtained with a
recently proposed technique which incorporates the complex
singular value decomposition (CSVD) of the data matrix. The
Bengough area is of particular interest due to a history of
unusual seismic activity. The CSVD algorithm does not
require the assumption of a pair of independent noise-free
signals, and the procedure readily separates the data into
noise and signal components from which the geophysical
transfer functions can be extracted.
A brief history and mathematical summary of the
magnetotelluric method are provided, and the data
acquisition equipment and procedure are described. The data
processing steps are outlined and some noise sources are
discussed. The results are interpreted with the aid of
digitized well-log data, apparent resistivity
pseudosections, and one-dimensional modeling based upon the apparent resistivity and phase curves obtained at each of
the five recording sites.
These results reveal a deep zone (at 10 to 15 km depth)
with a resistivity in the 50-75 Ωm range. The resistivity
of this conductive zone is significantly lower than the
values (1000-1500 Ωm) acquired from well-log resistivity
readings taken at the top of the Precambrian. There is a
general trend of decreasing resistivity in this deepest zone
from site to site, traveling west to east along the survey
line. Measurements taken at the west end of the survey line
reveal this zone has a greater depth (20 km) and higher
resistivity (250 Ωm) there than at sites to the east.
Without further observations to the west of the present
survey it cannot be concluded whether these measurements
mark the western edge of the NACP conductor or a more
gradual lateral change in its depth and resistivity.
It was felt that the CSVD method did not offer any
significant advantage over the cross-spectral computation
method, especially in light of recently introduced
improvements in data acquisition and processing techniques.
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Citation
Degree
Master of Science (M.Sc.)
Department
Physics
Program
Physics