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SEISMOLOGICAL OBSERVATORY GEOPHYSICS DIVISION DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH, WELLINGTON, New Zealand
Abstract
Detailed study of arrivals from accurately fixed earthquakes has revealed additional complexity in the travel-time curve for PKP. A notation is introduced in which observations are denoted by P' with a two-letter suffix indicating the branch to which they belong, namely P'AB, P'IJ, P'GH and P'DF. A new velocity solution for the Earth's core has been derived from these observations. This velocity solution differs from those previously suggested in having three discontinuous increases in velocity between the outer and inner core, at levels corresponding to 0.570, 0.455 and 0.362 times the radius of the core. This implies two shells, each between 300 and 400 km thick, surrounding the inner core; in each shell there is a small negative velocity gradient. The outer discontinuity is sufficiently shallow to prevent rays in the outer core from forming a caustic.
This article has been cited by other articles:
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  A. C. CHANG and J. R. CLEARY Precursors to PKKP Bulletin of the Seismological Society of America, August 1, 1978; 68(4): 1059 - 1079. [Abstract] [PDF]
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C. WRIGHT The origin of short-period precursors to PKP Bulletin of the Seismological Society of America, June 1, 1975; 65(3): 765 - 786. [Abstract] [PDF]
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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. D. ADAMS Multiple inner core reflections from a Novaya Zemlya explosion Bulletin of the Seismological Society of America, August 1, 1972; 62(4): 1063 - 1071. [Abstract] [PDF]
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