Spectral Analyses of High-Frequency P n and S n Phases Observed at Great Distances in the Western Pacific

Abstract

Both P n and S n phases recorded at distances greater than 3000 kilometers in the western Pacific have substantial amounts of energy at high frequencies, in some instances as high as 12 hertz for P n and 15 hertz for S n , A comparison of P n and S n spectra reveals generally higher energy levels and higher proportions of high-frequency to low-frequency energy for S n than for P n . Estimates of the effective quality factor, Q , indicate that the efficiency of S n propagation may be two or three times that of P n . First arrivals of P n and S n have apparent velocities in agreement with values for the uppermost mantle, whereas maximum-energy arrivals have apparent velocities in agreement with values for the lower crust.