Pattern Recognition and Tomographic Seismic Imaging Techniques with Applications to Subsurface Tectonic Structures of the Canadian Shield

摘要

Over the past few years a series of long range seismic refraction/wide-angle reflection and near vertical coincident reflection experiments were conducted across the Canadian Shield in eastern Canada. Crustal seismic near vertical reflection experiments have the potential of enabling us to view the subsurface crust in great detail. One of the limiting features of these studies is the poor signal to noise problems which often arise because of scattering and raypath lengthening effects which are caused by small scale lateral heterogeneities within the crust. In our studies, the conventional CDP imaging methods were replaced by much more powerful pattern recognition methods which were applied directly to the CDP gatherers. These methods produced dramatic improvements in the resolution of many of the major subsurface reflectors. Seismic refraction/wide-angle experiments which make use of multiple shots and hundreds of receivers enable us to study the crust from a different perspective. In conducting the tomographic analysis of the data to optimize the subsurface images, new methods of parameterizing the model for lateral heterogeneity were developed which employed triangular block methods coupled with delay time least squares inversion techniques. Greatly improved images were obtained when the regional vertical crustal velocity gradients were subtracted from the conventional velocity solutions to reveal velocity anomaly maps.