Abstract

Gravity measurements with La Costa-Romberg gravimeters were carried out in tall buildings on a floor-to-floor basis in New York City and in Armstrong Tower, Alpine, N.J. After corrections, the observed gravity versus elevation curves are nonlinear, particularly near the surface of the ground. The slope of the observed gravity anomaly versus elevation curves reverses sign at an elevation of about 170 feet for Columbia University buildings and about 350 feet for downtown buildings, and is nearly linear without a reversal for the Armstrong Tower. The vertical gradients vary substantially even within short distances. Comparisons are made of the corrected observed gradients with theoretical gravity gradients. The anomalous gradient anomalies are positive and are correlated with the positive isostatic surface gravity anomalies.

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