Delineation of basement surface relief from its magnetic anomaly using hybrid numerical algorithm

Abstract EN

Magnetic field mapping is a very powerful geophysical tool for recognizing basement relief.

In the present work, the problem of finding the depth to the basement surface is transformed into the problem of minimizing a constraint objective function ψ(zj) of the L1 norm instead of the traditional L2 in the unknown depths (zj).

The assumed subsurface model is consisting of a number of vertical prisms, homogeneously magnetized and of fixed magnetic susceptibility κ.

The Finite Difference-Quasi Newton (FD-Newton) algorithm with active set strategy (ASS) is used as a hybrid technique to minimize the constraint objective function ψ(zj).

Both linear and nonlinear bound constraints are implemented as a priori information to reduce ambiguity and improve the solution.

For simplicity, the problem can be solved as an even determined; however, it is directly solved as an over-determined with little modification The method is found to be stable, robust and convergent even for large size models and when implementing inherent noise in the synthetic examples.

Further, the present method is applied to a field example from the gulf of Suez, Egypt.

The calculated depths show a good agreement with results of drilled wells in that area.