Exploration Geophysics - Volume 14, Issue 1, 1983

Conventional contour maps of aeromagnetic data are often unsatisfactory for showing low amplitude anomalies or the more subtle changes in patterns associated with basement faulting. Simple one-dimensional filtering and differentiating techniques are used to obtain maps of the second horizontal derivative of magnetic intensity for the Broken Hill area, in order to enhance local features and reduce the effects of regional gradients. The second derivative is given as a three-level line-printer plot (maxima, minima and near-zero values), which minimises the contrast between areas of high and low magnetic relief. Closely spaced anomalies are resolved and trends related to basement faulting can also be inferred from the derivative maps. Lineations which are possibly several tens of kilometres in extent, and oriented mainly in northeasterly and northwesterly directions, may subdivide the basement of the Willyama Complex into a mosaic of blocks.

The electromagnetic (EM) mutual coupling ratio for a vertical coaxial loop system over a layered earth is expressed as a Hankel transformable integral. This expression facilitates the computation, using an available digital linear filter, for the response of either a perpendicular or a vertical coplanar loop configuration, or a Schlumberger electrode configuration. Such computations may be carried out on a programmable pocket calculator.