P-wave travel time residuals from the Alaskan aftershocks of 1964

Abstract

Travel time residuals of P-waves from 90 Alaskan aftershocks of 1964 have been studied. The data were selected from ISC bulletins. Altogether 9889 observations from 183 stations in the distance range 3 to 97° have been analyzed by a least-squares technique used by Cleary and Hales (1966a). In this way, deviations from the J-B tables have been separated from the station effect. The same method was subsequently employed to reveal the anomalies of azimuth and epicentral distance from the station residuals. Azimuth-distance dependent anomalies, called here the regional residuals, were calculated for 7° azimuth cells in the range 269 to 140°, and for 2° distance cells in the range 3 to 93°. Regional residuals distribution show some general features. Station residuals have been considered to three approximations: after separation from J-B travel time corrections, after removing the azimuthal effect, and after removing the distance effect. Station residuals to the third approximation are in general smaller from those to the first approximation, they do not show a marked regional trend and their frequency distribution is fairly normal. No evidence of any correlation with station height was found.