A near-vertical-incidence reflection survey conducted over the Precambrian Shield of Southeastern Manitoba

Abstract

A near-vertical-incidence reflection survey has been conducted in the Whiteshell area of southeastern Manitoba in an attempt to demonstrate the applicability of the method in investigating shallow crustal structure. Arrays of seismometers have been used to attenuate shot-generated surface waves. The degradation of random noise has also been achieved and the signal-to-noise ratio correspondingly increased. The use of detector arrays is recommended for all future reflection work carried out in Precambrian Shield areas. Boreholes have been drilled in granite gneiss and successfully used for the location of seismic sources. The ability to use predetermined shot points and thus attain a degree of freedom not otherwise possible, as when lakes, rivers, or abandoned mineshafts are used as source locations, has been demonstrated. The drilling of the boreholes is a time consuming and expensive process, although successful; it is recommended that patterns of surface charges be experimented with as a possible method of generating seismic energy. A velocity filtering program has been designed and the method demonstrated as being a reliable and efficient processing technique, capable of improving the signal-to-noise ratio. Velocities have been determined for direct wave arrivals. However, no near-surface structural features were observed.