Effect of magnetic field direction and source orientation on depth estimation solutions

Abstract

Most semi-automated processing routines assume simple scenarios where the resultant anomaly is produced by a single, parallel-piped, non-dipping source in a vertical ambient field. This however does not represent any realworld situation. All magnetic sources will have some dip and not be oriented parallel or orthogonal to the ambient magnetic field. Therefore, the angle at which the magnetic field intercepts the source will not be the same along all edges. This discussion is further complicated when one considers whether the source is 2D or 3D, which is dependent on where calculations are conducted along the source edge. This raises the critical question of how does the magnetic field direction affect depth solutions along the source edges which each have a different orientation? Tilt-depth has been shown to work reliably under ideal conditions. Since tilt-depth is a simplified formula using the assumption of a vertical magnetic field, one needs to revisit its fundamental equations. As it turns out, the fundamental equations that give rise to tilt-depth do employ basic magnetic field geometry parameters. This shows it is incorrect to assume that the same depth solution will be produced regardless of the source orientation relative to the magnetic field. The consequence of this effect becomes apparent through a solution asymmetry on either side of the source edge. By varying the field parameters in a synthetic scenario, it is shown that variable depth solutions are achieved depending on the planar orientation of the magnetic source.