Publication Date


Document Type


First Advisor

Ervin, C. Patrick

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology


Geology--Huron; Lake; Seismic reflection method; Seismic refraction method


A 46 kilometer portion of GLIMPCE reflection line J, corresponding to the entrance waters to Georgian Bay between Bruce Peninsula and Manitoulin Island, was reprocessed using an automated refraction algorithm. Both a lake bed correction and a refractor-offset correction were incorporated into the inversion of first arrival data to obtain a velocity-depth section along the profile. In the eastern third of the profile, the velocity-depth section is dominated by sub-horizontal refractors of probable Ordovician age. The gentle dip is consistent with the regional geologic structure, and the computed velocities are within the range of values expected on the basis of known lithologies in the area. Assuming that velocities on the order of 6.0 to 6.6 km/s mark the top of the Precambrian basement, the interpreted velocity-depth structure suggests that the depth of the westward-deepening basement surface ranges from 350 to 450 m. The western part of the profile track overlies near-surface, high-velocity Silurian dolomite, which tends to mask the refractions from underlying layers. In this instance, refractions from the basement surface become first arrivals beyond the limits of the shot-receiver spread length used. Also, refractions from the lake bed are often missed because the shot-to-first-receiver offset used was too large relative to the water depth. Because refractor depths are computed in a cumulative fashion, lack of information regarding the shallow layers precludes calculation of reliable depths for the deeper interfaces.


Includes bibliographical references (pages 122-132)


viii, 132 pages




Northern Illinois University

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