National Geophysical Data Grids: Gamma-Ray, Gravity, Magnetic, and Topographic Data for the Conterminous United States
by
Jeffrey D. Phillips, Joseph S. Duval, and Russell A. Ambroziak
1993 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director
The isostatic residual gravity anomaly data grid Isostatic residual gravity anomaly maps are produced by subtracting long- wavelength anomalies produced by masses deep within the crust or mantle from the Bouguer anomaly map. The long-wavelength anomalies are assumed to result from isostatic compensation of topographic loads. Isostatic residual gravity anomaly maps therefore reveal more clearly than Bouguer anomaly maps the density distributions within the upper crust that are of interest in many geologic and tectonic studies. The grid of isostatic residual gravity anomaly data (Simpson and others, 1986) was produced from the grid of Bouguer gravity anomaly data (Godson and Scheibe, 1982) by using an Airy-Heiskanen compensation model (Heiskanen and Moritz, 1967) with three parameters. The depth to the compensating root at sea level was chosen to be 30 km. The density contrast across the root was chosen to be 0.35 grams per cubic centimeter, and the density of the topography was chosen to be 2.67 grams per cubic centimeter. Other reasonable choices of these parameters would produce similar-looking residual maps. The computer program and topographic data sets used to produce the data grid were described by Simpson and others (1983a,b). The data were published in map form by Jachens and others (1985). Interpretations of the isostatic residual gravity anomaly map were presented by Simpson and others (1986) and by Jachens and others (1989). |
