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UNIVERSITY OF CALIFORNIA, BERKELEY, CALIFORNIA
Abstract
A set of travel times for the core-waves PKP is derived from observations and tabulated. All values are tied to the 1968 P travel times for a surface-focus for 75° < 
< 95° due to Herrin et al. Times for both the branches DF (110° < < 180°) and GH (125° < < 156°) are listed in more detail than previously, together with an extension for PKiKP waves, from 110° back to 105°. Checks on the DF branch for 120° < ° < 150° using observations from the 1965 LONGSHOT explosion provide no evidence for further revision of the first section of this branch.
Special attention is given to the times of the DF branch (PKIKP) for ° > 150°. Delays at 153° and 162° of order 3 sec reported by K. Ergin in 1967 are not confirmed. There is a group of small arrivals about 1 sec earlier than predicted by the present PKIKP tables for 156° < < 160°, approximately. These may indicate an error in the curvature of the present curve and, perhaps, a slight discontinuity in the inner core near a radius of 850 km. No evidence is found for a layer of any consequence with reduced P velocity in the inner core.
Revised times for the branch AB (denoted by PKP2) are based mainly on readings from the Indian Ocean earthquake of February 17, 1966 and the Jeffreys-Bullen times. For > 155°, the new empirical times confirm the curvature of the Jeffreys-Bullen curve for PKP2; however, near = 152°, the observed curvature appears to be greater than that of the latter curve. The new times are of the order of one second earlier; this result is highly sensitive to the precision of the epicenter estimated for the 1966 shock. PKP2 is traceable at least out to 185°.
Depth allowances for PKP have been computed, by T. Qamar, to provide a set consistent with the model Earth used by Herrin et al in the 1968 P tables.
This article has been cited by other articles:
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A. QAMAR Revised velocities in the Earth's core Bulletin of the Seismological Society of America, June 1, 1973; 63(3): 1073 - 1105. [Abstract] [PDF]
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J. H. WHITCOMB Asymmetric P'P': An alternative to P'dP' reflections in the uppermost mantle (0 to 110 km) Bulletin of the Seismological Society of America, February 1, 1973; 63(1): 133 - 143. [Abstract] [PDF]
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R. DATT and T. G. VARGHESE Array detection and location of core shadow events Bulletin of the Seismological Society of America, February 1, 1972; 62(1): 231 - 245. [Abstract] [PDF]
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 J. Oliver, J. Oliver, and L. Murphy WWNSS: Seismology's Global Network of Observing Stations Science, October 15, 1971; 174(4006): 254 - 261. [PDF]
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R. D. ADAMS Reflections from discontinuities beneath antarctica Bulletin of the Seismological Society of America, October 1, 1971; 61(5): 1441 - 1451. [Abstract] [PDF]
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G. G. R. BUCHBINDER A velocity structure of the Earth's core Bulletin of the Seismological Society of America, April 1, 1971; 61(2): 429 - 456. [Abstract] [PDF]
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M. NIAZI Source dynamics of the Dasht-e Bayaz earthquake of August 31, 1968 Bulletin of the Seismological Society of America, October 1, 1969; 59(5): 1843 - 1861. [Abstract] [PDF]
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E. HERRIN Introduction to "1968 seismological tables for P phases" Bulletin of the Seismological Society of America, August 1, 1968; 58(4): 1193 - 1195. [PDF]
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