LIMITATIONS OF DETERMINING DENSITY OR MAGNETIC BOUNDARIES FROM THE HORIZONTAL GRADIENT OF GRAVITY OR PSEUDOGRAVITY DATA

The horizontal-gradient method of Cordell (1979) and Cordell and Grauch (1985) assumes that density and magnetic boundaries can be piecewise approximated as single, near-vertical, sharp boundaries. The magnitude of the horizontal gradient of gravity or pseudogravity is maximum directly over this kind of boundary. When boundaries are not represented well by the vertical geologic-contact model, the location of the gradient maximum is offset from the boundary. For vertical boundaries that can be represented by the geologic-contact model of horizontal-slab model, there will be no offset. However, for thin, vertical dikes (d greater than w greater than equivalent to 0), the gradient maxima are always offset away from both edges.