New vertical seismic profiles from the northwest margin of the Sudbury impact structure provide details of structural geometries within the lower impact melt sheet (usually called the Sudbury Igneous Complex) and the sublayer norite layer. Vertical seismic profile sections and common depth point transformation images display several continuous reflections that correlate with faults and stratigraphic boundaries logged from drill cores. Of four possible mechanisms that explain repeated rock units, late-stage flow or normal faulting that occurred within the last layers to cool and crystallize might best explain the observations, especially the most prominent reflectors observed in the seismic data. These results reaffirm previously proposed two-stage cooling and deformation models for the impact melt sheet.
An acoustic velocity logging probe has been used to acquire data on the seismic characteristics of the McConnell nickel deposit in the Sudbury area. Preliminary results indicate good velocity contrasts in the stratigraphic sequence associated with the massive
sulphides. These velocity contrasts are related to the density and elastic properties of the rocks; density was measured in the same borehole with a density logging probe. One interesting observation is that the high density massive sulphides have low P-wave velocities relative to the host rocks.
This is not a universally applicable condition because some massive sulphides in other areas being investigated have higher velocities. Full sonic waveforms were recorded and these will be further studied to extract S-wave velocities. The P- and S-wave velocity and amplitude logs will then be used
to derive valuable geotechnical information.
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