SEMI-DIURNAL EARTH TIDAL COMPONENTS FOR VARIOUS EARTH MODELS
LAMONT GEOLOGICAL OBSERVATORY PALISADES NY
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This study of the elastic deformation of the earth due to tidal- generating potentials attempts to evaluate the possible cause for the discrepancy between the accumulated observational data of earth tides for the principal semi-diurnal tidal constituent, M sub 2, and the theoretical values. The characteristic numbers, h, k, and l of the earth are calculated for earth models consisting of velocities due to Jeffreys or Gutenberg with Bullen A or Bullen B density distribution. The computations were made using a modification of an earlier program for an IBM 7090 written for calculating the free periods of the earth. The characteristic numbers of the earth are nearly independent 1 of the presence of the solid inner core for a wide range of the possible values of the outer core rigidity 2 of either the Jeffreys or the Gutenberg velocity models, i.e., of the presence or absence of a low velocity channel in the upper mantle. A comparison of the theoretical gravimetric factors G calculated for a continental and an oceanic earth model with the observed gravimetric factors of the semi-diurnal tidal constituent, M sub 2, obtained principally during the International Geophysical Year indicates that the differences in the observed values of G appear to be primarily due to the effects of the ocean and only secondarily to differences in the variation of the crustal structures.
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