Gravimetric Prospecting

a method of exploratory geophysics, based on the study of the earth’s gravitational field. The principal condition for the use of gravimetric prospecting is that there be variation in the densities of the rocks making up a geological structure that is capable of creating anomalies in the observed gravitational field of the earth.

Gravimetric prospecting identifies structures that are hidden by sedimentary rocks and thus are inaccessible for study by conventional geological methods. As a result of gravimetric surveying to determine the qualitative estimates of the gravitational field, it is possible to identify both areas that are promising for mineral exploration (general gravimetric prospecting) and particular geological structures that may contain petroleum, gas, or various kinds of ore deposits. In detailed gravimetric prospecting local anomalies in the gravitational force are studied carefully to determine the conditions and elements of occurrence of the objects forming the anomaly (depth, shape, and dimensions). In most cases the results of study are ambiguous: an infinite number of different distributions of anomalous masses can be selected that would create the same gravitational anomaly. An unambiguous solution may be found by making certain assumptions about the anomalous masses and by using geological data and deductions from other geophysical methods. Gravimetric prospecting is usually combined with magnetic, electrical, and seismic prospecting. Along with observed gravitational anomalies gravimetric prospecting often uses various derivatives obtained from them by conversion or identical gravitational anomalies corresponding to points above and below the earth’s surface. The process of conversion is called transformation of the gravitational field. Particular geological structures may be identified better by the qualitative character of the transformed gravitational field. Under favorable conditions transformation makes it possible to determine the depth of occurrence and the shape of particular geological structures. In order to solve problems of gravimetric prospecting, gravimetric surveys are conducted, which are subdivided according to the conditions under which they are made into land surveys, ocean surveys (surface, underwater, and sea floor), underground surveys, and aerial surveys. The data of gravimetric surveying are used in studying the deep-seated structure of the earth.