Tau estimates for mantle P- and S-waves from global travel-time observations

Travel-time data from the ISC Bulletin were used to determine a τ(p) confidence region for mantle P- and S-waves. One year of P data, amounting to approximately 108000 travel times, and four years of S data, amounting to approximately 75000 travel times, were used. Geometrical path corrections were applied to place all sources and receivers at a common radius of 6338 km. A preliminary test was devised and applied to the travel-time data to determine if they were suitable for the estimation of τ(p). This criterion precluded construction of complete tau functions for the mantle, particularly the upper mantle. Thirty-five confidence intervals for the mean τ(p) were computed at the 99.9 per cent confidence level from the P data, and 23 were computed from the S data. Most confidence interval widths were less than 0.2 s for P-waves, and less than 0.8 s for S-waves. Comparison with computed τ(p) for several published velocity models indicates significant differences among the models in the τ(p) domain.