Earthquake Waves Reflected at the Inside of the Core Boundary*

-Travel times of waves generated by an earthquake at a depth of 600 km and reflected from the inside of the core boundary as well as the epicentral distances of the caustics of PKKP, SKKP, and PKKS agree within the limits of error with those calculated on the basis of velocity-depth curves. This applies also to the travel times of SKKS and SKKKS for which poor agreement was reported before the inner core was established. The periods of all waves traveling through the outer core seem to be shortened. In the outer core the attenuation is possibly smaller than in the mantle. Symbols and materials used--For brevity in the following discussion, waves which have traveled through the outer core, but not through the inner core, are indicated by one prime, those which have entered the inner core, by two primes. Thus, for example, P' • PKP, P" • PKIKP, SKKP" = SKIKKIKP. Symbols with a subscript i (for example, P•') refer to the earlier of two branches connecting at a focal point, those with a subscript 2 to the later. An asterisk indicates an epicentral distance over 180 ø (for example, SKKS*). Unless it is stated otherwise, all data refer to the earthquake of 1957, April 16, 4:04:04, with an adopted epicenter at 4.5øS, 107.5øE, focal depth 600 kin. The elements of tl•s shock have been redetermined. Considering the expected systematic errors involved in the calculation (for example, in the assumed travel times or resulting from the assumption that the internal structure of the earth is spherical), the coordinates of the adopted epicenter are probably correct within a few tenths of a degree, the origin time within 2 or 3 seconds, and the focal depth within about 20 km. Records of this shock from 55 stations at distances from 119 ø to 178 ø have been used previously by Gutenberg [1958a, p. 244]. Additional records have been made available upon request by the following stations (epicentral distance in degrees in parentheses): Brisbane * Contribution No. 933, Division of Geological Sciences, California Institute of Technology. (48.9), Matsushiro (49.9), Jerusalem (77.4), Kiruna (93.0), Uppsala (93.8), Honolulu (95.7), Skalstugan (96.3), College (100.3), Sitka (108.1), Alberni (117.3), Victoria (118.5), Banff (121.3), Saskatoon (124.8). The author is very grateful for the speedy response from all stations. Theoretical travel times of waves originating at the earth's surface have been calculated on the basis of the tables of Jef]reys and Bullen [1940] for waves through the mantle. For those through the core the same procedure has been followed as described by Gutenberg [1958a, p. 241]. This is based on the travel times of Gutenberg [1958b, Table 4] for the portion of the waves through the core and on the travel times of Jef]reys and Bullen [1940] for PcP, ScS, and ScP for zero focal depth. Corrections for the focal depth of 600 km have been taken either from tables of Jef]reys and Bullen [1940] or from tables of Gutenberg and Richter [1936]. The resulting differences between the two procedures are small and within the limits of errors. Corrections for the effect of the focal depth on distances of the focal points have been taken from tables of Gutenberg and Richter [1936]. Errors in the assumption of corresponding portions of PcP, ScS, and PcS on the one hand and of the portions of the paths inside the core on the other rarely affect the resulting travel-time curves by more than 2 seconds; moreover, they may shift the calculated distance of focal points by