Hardrock seismic imaging

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In heterogeneous (hardrock) environments such as the Canadian Shield, a number of parameters related to scale and composition need to be considered that render seismic studies more problematic. To model the propagation of seismic waves in these areas requires knowledge of petrophysical parameters (compressional and shear wave velocities and densities) and their distribution within the crust, which can be derived directly from borehole logs (in 1-D) or indirectly from geological maps and lithological analysis. We will collect velocity and density logs from various sources and analyze them for their first and second order statistics. These not only give us the 1-D parameters in the vertical dimension but by correlating several boreholes will provide the means of constructing a 3-D model of crustal heterogeneity. Added to the background model will be massive sulfide deposits, which are known to scatter seismic energy according to their shape, size and composition. 3D elastic/visco-elastic forward modeling studies will be used to optimize 3D surface and borehole seismic data acquisition strategies. In addition, heterogeneities may cause attenuation. As waves travel in heterogeneous media, they lose energy with distance and time due to spherical divergence and absorption. It is commonly accepted that a flat absorption band exists for the solid earth. The effects of absorption and dispersion have been observed in exploration seismology at various frequencies (i.e. surface (Hz), borehole (KHz), and laboratory seismics (MHz)) for some time. We will use uncorrelated (raw) Vibroseis data to measure velocity dispersion and attenuation in the exploration seismic frequency band. Ongoing research projects will focus on unique pressure-temperature conditions (and mineral deposits) related to meteorite impacts (Bosumtwi, Ghana; Chicxulub, Mexico; Sudbury, Ontario; Wanapitei, Ontario; the physical properties of permafrost and gas hydrates (Mallik, NWT) and 3D seismic research projects for deep mineral exploration (Ontario, Quebec and New Brunswick).