This research is to analyze shear-wave splitting in the upper mantle in two areas in western South America, a volcanic area southwest of Bucaramanga in western Colombia, and a large non- volcanic area in central Peru. This analysis will involve data from both local and teleseismic earthquakes and will be used to compare to results obtained at Bucaramanga where splitting was ascribed to a wedge-shaped anisotropic volume in the upper mantle immediately above the Wadati-Benioff zone, especially in a volcanic versus a non-volcanic setting. The results will bear on models of deformation of the mantle due to the subducting slab and thereby on the mechanism of earthquake generation in one of the world's most active seismic areas. This research is a component of the National Earthquake Hazard Reduction Program.
