IMAGING AND INTERPRETING THE SHALLOW CRYSTALLINE CRUST

In the past, many tests of high-resolution seismic imaging methods, ut ilizing 'off-the-shelf' technology from hydrocarbon exploration have h ad only limited success. Some problems associated with the application of seismic profiling in the shallow crystalline crust differ from tho se encountered in sedimentary basins. Perhaps the most fundamental dis tinction stems from differences in statistical properties of the refle ction coefficient time series. Analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crysta lline crust are depleted in the seismic bandwidth relative to sediment ary basins. This fundamental difference must be considered in the desi gn of shallow crustal seismic surveys in order to achieve success. To a first approximation, acoustic impedance variations in sedimentary ba sins are controlled by velocity changes, whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity. In cert ain instances, density fluctuations outweigh velocity fluctuations. Fo r example, physical rock property data from mining districts in the Ca nadian Shield suggest that massive Fe-oxide or sulphide bodies will ge nerate strong seismic reflections. (C) 1998 Elsevier Science B.V. All rights reserved.