Corine Prieto, 1998. "Gravity/Magnetic Signatures of Various Geologic Models—An Exercise in Pattern Recognition", Geologic Applications of Gravity and Magnetics: Case Histories, Richard I. Gibson, Patrick S. Millegan
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In every geologic province, the physical parameters are unique. The prospective anomaly signature associated with each individual area will vary accordingly. The pattern recognition of an anomaly signature is of vital importance to all interpretation sciences. The following discussion is intended for geophysicists and geologists interested in obtaining a working knowledge of what type of signal pattern should be observed to integrate gravity and magnetic data with seismic and geologic data for development of exploration targets. The incorporation of the integration process in exploration has been known to reduce risk and therefore reduce the total cost of exploration.
The gravity and magnetic anomaly signature characteristics are results of one or more physical parameters such as the configuration of the anomalous zone, density, velocity, and porosity contrasts, magnetic susceptibility contrasts, and the depth to the anomalous body. An excellent tool to aid in pattern recognition is structural modeling. A simple collection of geologic structures has been modeled and their calculated gravity and magnetic responses are discussed to identify anomaly characteristics. The collection is not intended to be a library of curves, but rather an exercise in pattern recognition. The 2-D modeling scheme used an interactive graphic system. The well-known Talwani algorithms (see references) were used as the basis for the computations.
The density and magnetic susceptibility contrasts are based on data from various geographic areas from the Superior Oil Company exploration cases and from published literature. The structures of the models have been kept simple to emphasize how depth, density, and susceptibility
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The idea for this book came from a perceived lack of recent, instructive examples of exploration-oriented interpretations of gravity and magnetic data. The Society of Exploration Geophysicists two volumes, Geophysical Case Histories, are probably closest in philosophy to this book. Published in 1948 and 1956, many of the examples in the Case Histories are relatively dated and specific to particular areas. We hope this new book provides an update that includes lessons about gravity and magnetic exploration that can be applied to many parts of the world. The Utility of Regional Gravity and Magnetic Anomaly Maps (SEG, 1985, W.J. Hinze, editor) contains some excellent papers dealing with tectonics that have clear bearing on hydrocarbon exploration, but no paper shows the relationships among hydrocarbon accumulations, exploration, gravity, and magnetics. Geophysical texts focusing on gravity and magnetics, including L.L. Nettleton's classics, include only a few (albeit often excellent) case histories, and many are dated.
Thus, this book's target audience is geologists and geophysicists in operations offices, actively involved in exploration at any level from basin analysis to prospect generation. Although most of the papers deal with hydrocarbon exploration, several papers relate to gravity and magnetic data in mining and environmental applications. A final section is included on new developments, the state of the art.
The book is not intended for gravity and magnetics specialists (although we hope they will find it interesting), or for geophysicists interested in theory, acquisition, and processing, unless those aspects are important to the geologic exploration problem and to the decisionmaking process.
We believe that the philosophical approach to interpretation is almost as important as some aspects of a technical interpretation itself. This book reveals the diversity of philosophies that gravity and magnetic interpreters embrace, as well as the common threads to which all interpreters aspire.
This book is not a textbook, although we have tried hard to highlight the exploration lessons inherent in each technical paper. Additional instructional aspects of the book are the glossary of gravity and magnetic terms, provided by Integrated Geophysics Corporation (with assistance from Richard Hansen of Pearson, DeRidder & Johnson) and an annotated bibliography, which has pointers to the rich literature of gravity and magnetics. Other short "lessons" can be found in stand-alone illustrations or short features throughout the book.
We thank Ray Thomasson for continual encouragement, suggestions, and prodding. Reviewers, whose efforts are appreciated greatly, include Dale Bird, Bill Pearson, Mark Odegard, and several anonymous reviewers. We appreciate the help of the AAPG, especially Ken Wolgemuth, in this, the first effort at serious book publication by the coeditors.