Investigation of Factors Affecting the Transportability of the P/S Amplitude Ratio Discriminant

Abstract : The research under this program has investigated problems associated with transporting regional-phase amplitude ratios, such as Pn/Sn or Pn/Lg ratios. The first study investigated the effect of sensor site effects on the variance of P/S ratios. Using multiple array recordings of groups of events in the same source region, we characterized the factors that contribute bias or the scatter of P/S ratio measurements, after correction for propagation path effects. The variance in the P/S ratio around regional arrays reveals the extent to which site affects cause variations in P/S ratios. The partitioning of the variance between source, path, and receivier effects was examined by analysis of variance (ANOVA). In the second study, we performed a statistical analysis of the transportability of P/S ratio discriminates using separability measures and optimum transformations in order to reduce dimensionality of multiple frequency P/S ratios. These transformations consist of calculating the intra-class, and inter-class scatter matrices for P/S ratio discrirminants and using the eigenvectors, corresponding to the largest eigenvalues of,the inter-class matrix to compute optimum transformation of discriminants that provide the best separation. We applied this analysis to distance-corrected,discriminants in different regions (e.g., China,'Eurasia, North A,merica) in order to compare discriminant effectiveness for different regions and to evaluate the transportability of optimum discriminant decision surfaces.