DIFFRACTION OF P BY THE CORE: A STUDY OF LONG-PERIOD AMPLITUDES NEAR THE EDGE OF THE SHADOW

Theoretical expressions for the amplitude of P-waves in the neighborhood of the core shadow boundary have been formulated and evaluated by computer. Comparison with 2.5 second data of Sacks confirms his determination of the shadow position at 96.5 degrees. A square root frequency scaling law is foun...

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Bibliographic Details
Main Authors: Phinney, Robert A, Cathles, Lawrence M
Format: Report
Language:English
Subjects:
AMPLITUDE MODULATION
CORE(EARTH)
DIFFRACTION
EARTHQUAKES
FUNCTIONS(MATHEMATICS)
GEOMETRIC OPTICS
HIGH FREQUENCY
MATHEMATICAL MODELS
PENETRATION
PHASE STUDIES
PRIMARY WAVES
PROPAGATION
SECONDARY WAVES
SEISMIC WAVES
Seismology
SOURCES
THEORY
VELOCITY
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Summary:Theoretical expressions for the amplitude of P-waves in the neighborhood of the core shadow boundary have been formulated and evaluated by computer. Comparison with 2.5 second data of Sacks confirms his determination of the shadow position at 96.5 degrees. A square root frequency scaling law is found for the high frequency diffraction pattern, and permits use of the Fresnel integral function at short periods. Long-period amplitude data for three paths have been spectrum analyzed and compared against the theoretical amplitude dropoff going into the shadow. The agreement is about as good as the data will permit, and no indication is found at these periods of a low-amplitude defocused region at 90 degrees to 96 degrees, after diffraction has been accounted for.