Most regional discriminants developed to date have been based purely on empirics, and many rely on the characteristics of spectra. At Woodward Clyde, a unique type of time domain discriminant has been developed based on a theoretical understanding of wave propagation and the direct identification of depth phases in P sub n and Pg. This work has involved original basic research into the nature of the short period P sub n waveform and the effect of pP sub n on it; development of an understanding of the nature of P sub n propagation; and inquiries into the relation of pP sub n and spall. The studies of Pg have involved identification of a frequency band in which the waveform is stable; a forward modeling study of NTS regional data; and a careful breakdown of the wavenumber integration synthetics into the generalized rays that compose them. This work has led to direct identification of depth phase effects in Pg and a preliminary indication of how to detect and discriminate with them. This is the first report on a multi-year effort to complete development of the P discriminants, to extend the technology to S sub n and Sg and to test the power of the discriminants on the new data bases from the Soviet Union. Strong efforts to analyze the new data from the Soviet Union have been undertaken including studies of both the older hand digitized analog records and of the digital data from the new IRIS stations.