A reconnaissance of tidal gravity in southeastern United States

Abstract

Tidal variations of gravity were measured at 10 locations in southeastern United States. The spatial variation of tidal gravity is indicated by relative gravimetric factors δM2 and δO1 and gravimetric factor ratios δM2/δO1 obtained from the lunar semidiurnal and diurnal tidal gravity constituents. The following values of δM2/δO1 were obtained from harmonic analyses of tidal gravity records: 1.006 ± 0.006 at Atlanta, Georgia; 1.026±0.004 at Blacksburg, Virginia; 1.028±0.007 at Columbia, South Carolina; 1.038±0.008 at Durham, North Carolina; 1.019±0.005 at Huntington, West Virginia; 0.989±0.012 at Jackson, Mississippi; 0.988±0.007 at Memphis, Tennessee; 0.991±0.009 at Ruston, Louisiana; 0.995±0.011 at Tuscaloosa, Alabama; and 1.011±0.007 at Wooster, Ohio. The uncertainty estimates are mean square errors calculated individually for each tidal gravity record. The ocean tide is known to be the principal cause of spatial variations of tidal gravity. This effect is examined through comparison of measured gravimetric factors and ratios and corresponding values predicted from five different published cotidalcorange charts of the M2 constituent of the tide in the world ocean. These charts were prepared from numerical solutions of the Laplace tidal equations. In one the effects of earth deformation and ocean self-attraction are considered, whereas in the second, only earth deformation corrections are made. Neither of these effects is considered in the other three charts. Patterns of spatial variation of tidal gravity over the study area predicted from these models of the global M2 ocean tide are clearly distinguishable one from another. Comparisons with the measured pattern of spatial variation indicate that measurements of tidal gravity in interior regions of continents can be used to discriminate between different models of the global ocean tide.