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Abstract

A complementary pair of wavelength-filtered regional and residual gravity maps of the United States has been compiled from a digital gravity base. Processing of simple model anomalies with the same filters as those used on the maps shows that the short-wavelength (SWL) anomalies, although exaggerated in shape and distorted in amplitude, give a clearer indication of source geometry than the total-field Bouguer anomalies. Side lobes created by the filtering process appear to be the most serious deficiency of the SWL maps, but they can often be distinguished by using simple criteria. The model studies also show that the horizontal-gradient amplitude map is a useful adjunct for interpreting the SWL anomalies. Maximum horizontal-gradient/amplitude relations indicate that most of the anomalies of the SWL map, particularly the prominent ones, have their source in the crust. There is considerable leakage of long-wavelength (LWL) energy from relatively narrow but intense anomalies into the LWL field so that moderate-wavelength anomalies in the LWL map must be interpreted with care. The SWL map defines a series of zones that are based on anomaly characteristics, primarily anomaly trend. These zones correspond in many places to previously identified geologic terranes. It is concluded that rift systems can account for many of the SWL gravity features of the eastern United States; a model of a rift deformed by compression is proposed to explain many of these features. Other gravity-geologic correlations, notably over igneous features, are discernible.

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