This research is to utilize the polarization direction of short period P waves to investigate lateral heterogeneities in the lithosphere. Recent measurements of the polarization direction have shown that stable results can be obtained with a precision of about 5 degrees, and that these directions are sometimes systematically different from ray theoretical predictions based on a laterally homogeneous compressional velocity structure. Lateral heterogeneities mapped by means of the polarization direction anomalies have the potential to delineate velocity anomalies associated with active fault zones. This research is a component of the National Earthquake Hazard Reduction Program.
