The Utility of Regional Gravity and Magnetic Anomaly Maps

Abstract

Mapping of the Earths gravity and magnetic fields has a long and distinguished history as part of the investigations of the structure and petrologic variation within the Earths lithosphere. Prior to 1950, observations of anomalies in these planetary fields had gene rally been focused on limited areas for specific mineral-resource and geological objectives. The increasing availability of portable gravimeters and the development of aeromagnetic-survey technology shortiyafter World War II, however, led to efficient and precise gravity and magnetic mapping of extensive regions. These regional surveys were conducted for the most part by governmental organizations most of ten as a means of evaluating or stimulating the exploitation of earth resources. The data from these federal surveys are generally available in the public domain and have been augmented by large amounts of data collected by academic institutions for basic-research investigations. Vast amounts of gravity and magnetic-anomaly data also have been acquired by industrial firms in mineral-resource exploration, but with few exceptions these data are generally not available to the public. In the United States, the publicly available data have recently been composited into new or improved country-wide anomaly maps. In 1975, the Society of Exploration Geophysicists (SEG) and the U.S. Geological Survey, recognizing the value of regional gravity and magnetic-anomaly maps, jointly organized gravity-and magnetic-anomaly map committees to prepare anomaly maps of the United States. The immediate objective of the committe es was to compile and publish a revised gravity-anomaly map of the conterminous United States and the first magnetic-anomaly maps of the conterminous United States and Alaska. These objectives were met in late 1982 with the publication of the Gravity Anomaly Map of the United States by the SEG and the release of the Composite Magnetic Anomaly Map of the Conterminous United States and the Magnetic Anomaly Map of Alaska by the U.S. Geological Survey. Small-scale versions of these maps are reproduced in color in this volume together with the most recently published gravity-and magnetic-anomaly maps of Canada. In recognition of the publication of these national maps, and to illustrate the many uses of gravity-and magnetic-anomaly maps, aseries of special technical sessions was held at the 52nd Annual International Meeting of the SEG in the fall of 1982 in Dallas, Texas. A total of 33 of the 53 papers presented at the special sessions were accepted for publication in this volume, The Utility of Regional Gravity and Magnetic Anomaly Maps.