SOME REMARKS ON STATIC-FIELD THIN SHEET MODELS

Two thin sheet models are considered which are efficient in calculating electric or magnetic anomalies of thin formations whose material properties satisfy certain limit conditions. The first model is valid when the contrast in physical parameters between the sheet and its environment is very low, and has been widely used in magnetic modelling of mineralized veins and dikes. The second model applies at very high contrasts in physical parameters, and is superior in modelling very thin bodies, which are difficult to treat using conventional three-dimensional surface integral equations. This model is most applicable to electrical modelling of massive mineralized veins. In the low-contrast model, the anomalies are produced by dipolar sources aligned both normal and parallel to the sheet. If the primary field has both a normal and a longitudinal component, the anomaly over a vertical sheet represents the superposition of an antisymmetric and a symmetric component. The sources of this model are homogeneous and they can thus be solved using the demagnetization factors technique. When the contrast in material properties is very high, the sources normal to the sheet vanish, and the anomaly is represented entirely by the longitudinal field in the sheet. Independently of the alignment of the primary field, the vertical secondary field over a vertical sheet is always symmetric. The source density along the sheet is now highly inhomogeneous, and a special algorithm has to be used in its solution.