Semi-automatic determination of dips and depths of geologic contacts from magnetic data with application to the Turi Fault System, Taranaki Basin, New Zealand

We show a simple and fast method for calculating geometric parameters of magnetic contacts from spatial gradients of magnetic field data. The method is based on well-established properties of the tangent of the tilt-angle of reduced-to-the-pole magnetic data, and extends the performance of existing methods by allowing direct estimation of depths, locations and dips of magnetic contacts. It uses a semi-automatic approach where the user interactively specifies points on magnetic maps where the calculation is to be performed. Some prior geologic knowledge and visual interpretation of magnetic anomalies is required to choose proper calculation points. We successfully tested the method on synthetic models of contacts at different depths and with different dip angles. We offer an example of the method applied to airborne magnetic data from Taranaki Basin located offshore the North Island of New Zealand.