Automatic forward modelling of two-dimensional problems in electromagnetic induction

finite difference algorithm for solving the forward modelling problem of geo-electromagnetic induction in two-dimensional (2D) structures has been developed in this thesis. The governing equations have been modified to solve for the anomalous field by separating out the 'host' field which is assumed to be the field generated by the one-dimensional (1D) conductivity distribution on the left hand side of the model. This was done to prevent the small anomalous fields being masked by the much larger host field due to the finite length of the computer word. One of the most important features of this program is an automatic gridding subroutine which greatly reduces the amount of time required to design a suitable grid for a model and removes the human element from such grid design. Up to 20 periods can be submitted to the model at one time and specific locations (e.g. the locations at which field data are available) can be added to the automatically generated grid. Integral boundary conditions at the surface and bottom (z = d) of the model eliminate the need to extend the grid above the earth's surface or down into the half-space underlying the model.;The program has been used to perform a 2D inversion of magnetotelluric data from a NS profile in Sardinia. The magnetotelluric responses from two sites along this profile indicated that the structure underneath them could not be considered to be solely 2D. To examine the conductivity anomalies perpendicular to the profile that are affecting the results at these two sites, 2D inversions were performed on the data to obtain their EW conductivity models. The apparent resistivity curves from the models fit the data fairly well at both sites especially at short periods. Many features of the models were in agreement with the 2D model along the profile obtained by Peruzza et al. (1990) and they also provided insight into the geological structure of the area.;A study was made of the behaviour of 2D induction arrows over a buried conductivity contrast. Although the general trend of in-phase arrows is to point towards the regions of high electrical conductivity, some investigators have found small amplitude in-phase arrows that point away from these same regions. Reversals such as these, which do not behave according to the general trend, can cause confusion and erroneous interpretation of the in-phase induction arrows.;Finally a 2D inversion scheme was discussed in which a 2D forward modelling program was incorporated with a minimization routine MINDEF. First an investigation was made into the relative merits of using the impedances...