Application of both the horizontal gradient magnitude (HGM) and analytic signal (AS) methods to the magnetic data yields more geologic information than is obtained, when either method is used individually. The positions of maxima in the HGM and AS are useful for identifying surface locations that lied directly above the edges of source bodies. The AS maxima occur directly over the edges, while the HGM maxima are generally offset down dip from the true locations of the edges of the source bodies, when the structures are not vertical. The two methods can, therefore, be employed together to identify the accurate locations of contacts.
Aeromagnetic data for Wadi Um Balad area, north Eastern Desert, Egypt, were analyzed using this approach. Two automated interpretation methods, horizontal gradient-depth (HDEP) and analytic signal-depth (ASDEP), as implemented by Phillips (1997), were used for the grids of HGM and AS to determine the magnetic contacts with their strikes and depths, as well as the down dip of the dipping contacts. Overlying the two resulting data sets was done to construct a depth-contact location map, which provides a skeletal outline of what may be interpreted as contacts between units of different magnetizations. This map reveals three major sets of structural lineaments trending mainly in the NW-SE, NE-SW and NNW-SSE directions, beside minor sets trending in the N-S, NNE-SSW and E-W directions. On the other hand, depth estimates showed a range of values that seem plausible with the configuration of the outlined causative sources. It is obvious that, the depth values (42-400m) are concentrated above the tops of the outcropping basement rocks at the eastern part, whereas the deep ones reaching 2.2 km are deviated outwards in the central and western parts of the area above the sedimentary rocks..