Executive Corner
Applicability of Gravity and Magnetic Techniques
by Dick Gibson
by Dick Gibson
The utility and value of gravity and magnetics today are greater than ever, because of their low cost compared to seismic data and drilling, availability of many continent-scale data sets for tectonic analysis, and increasing resolution through advanced acquisition and processing techniques. Subtleties in gravity and magnetic data can be used to define salt in the Gulf of Mexico and even local channels containing sediments that have different magnetic or density character. Tectonic studies can indicate areas of likely structural development and even possible likely zones of fracturing. Especially in new international frontiers (China, southeast Asia, Former Soviet Union), these low-cost data should play a significant role in planning exploration strategy. Even in U.S. basins, the information content of a high-resolution survey is often significantly greater than the "traditional" use of gravity (major structures) or magnetics (basement depths). Magnetic surveys are common adjuncts to mineral exploration and exploitation programs, often integrated with advanced electrical techniques.
Magnetic data still find their greatest application in mapping buried metallic objects, but excellent magnetic surveys have been used archeologically to define teepee rings, hearths, and other structures. Similar approaches may contribute to understanding soil and channel distribution in aquifers and other environmentally interesting situations. Gravity data can help locate buried void spaces, as well as assisting in the delineation of subsurface features like channels. A high-tech superconducting gravity meter exists that can discern between a "filled" aquifer and a mostly empty one.
The advent of abundant low-cost regional data sets (e.g., published US gravity and magnetic maps, and others around the world) makes them a reasonable and vital adjunct to tectonic, structural, and seismological studies. My recommendation to geologists is "just look and see" if there are any interesting correlations in these data with whatever it is you are studying.
Gravity and magnetic maps are pretty!
