Regional free air gravity anomalies and tectonic observations in the United States

Abstract

Four free air gravity maps of the United States have been constructed from mean free air values in areas of 6×10 2 km 2 (one 15′ quadrangle), 7.5×10 3 km 2 (12 quadrangles), 6×10 4 km 2 (99 quadrangles), and 6×10 5 km 2 (945 quadrangles). The technique of averaging free air values in successively larger areas is a simple filter which eliminates short wavelengths. The maps derived from land data can be used for comparison with the long‐wavelength free air field derived from satellite data. An excellent correlation is observed between the 6×10 5 ‐km 2 map and recent satellite maps. The dominant regional anomalies in the United States are the following: (1) the arcuate positive extending from the Appalachians, through the Gulf Coast inner continental shelf and northward along the Rio Grande Rift and Front Range, (2) the sinuous, midcontinent low extending from Wisconsin through Texas, (3) the Columbia Plateau minimum, (4) the Basin and Range and Salton Sea minimum, and (5) the positive over the Colorado Plateau. We suggest that the local gravity anomalies displayed by Bouguer gravity maps and the free air maps of 1‐ and 12‐quadrangle averages are caused by mass distribution in the lithosphere of some antiquity, whereas the regional anomalies are caused by deformation of the lithosphere which is in turn related to contemporary plate dynamics.