FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹

Abstract

Among electromagnetic sounding techniques, the Mélos method possesses the specific feature of including an apparent resistivity computation. This acts as a normalizing scheme so that 2D modelling results can be obtained without accounting for a true 3D source. However, in order to get reliable numerical modelling results for a 2D magnetic dipole source, improved algorithms are required in order to apply the standard finite‐element technique: quadratic basis functions must be used in place of linear basis functions, and a more sophisticated method than conventional ones is necessary for properly solving the resulting system of linear equations. Such modelling results have been used to study theoretical responses for the Mélos method in the search for conductive bodies in mineral exploration. Two sets of models are presented and discussed. They show that the typical Mélos response to a conductive target is a bipolar anomaly on the apparent resistivity pseudo‐section, with a conductive pole at low frequency which is centred above the target.

Electromagnetic 2.5-dimensional forward modelling with a boundary integral formulation

“…Besides the boundary integral formulation, two other solutions of the Maxwell equations are the finite‐element method and the domain integral formulation. The finite‐element method is well known and its advantage lies in the very sparse, symmetric and positive‐definite matrix of the linear system to be solved ( Valla 1992). The dimension of the linear system is related to the number of surface elements and may be high.…”