Detection, analysis, and interpretation of teleseismic signals: 1. Compressional Phases from the Salmon Event

The travel times and amplitude spectrums of first- and later-arrival P phases from the Salmon event are computed on the basis of polarization filter outputs. The interpretation of the P wave radiation field is made in terms of crust and mantle structure using the first- and later-arrival P phases and their amplitude spectrums. The observed seismic field corresponds with that expected from a symmetric, purely compressive source. The essential features of the observed travel times and amplitudes are explained in terms of regional mantle structures. These structures provide first-order fits to the observed data and are characterized by low-velocity zones which terminate with rapid and continuous increases in velocity near depths of 130 km. The velocity structures also show a strong velocity gradient near 330 km. The regional models differ most strongly in the relative extent and magnitude of the velocity decrease in the Iow-velocity zone.