Magnetic interpretation using the 3-D analytic signal

TLDR

The method defines the 3‑D analytic signal as the square root of the sum of squared vertical and horizontal magnetic field derivatives, uses a half‑width rule to estimate depth from vertical contacts, and is illustrated on two examples. The 3‑D analytic signal produces maxima over magnetization contrasts that delineate source outlines independent of ambient field, as demonstrated by revealing a possible impact crater beneath Lake Huron and mapping terrane continuation across the Cabot Strait.

Abstract

A new method for magnetic interpretation has been developed based on the generalization of the analytic signal concept to three dimensions. The absolute value of the analytic signal is defined as the square root of the squared sum of the vertical and the two horizontal derivatives of the magnetic field. This signal exhibits maxima over magnetization contrasts, independent of the ambient magnetic field and source magnetization directions. Locations of these maxima thus determine the outlines of magnetic sources. Under the assumption that the anomalies are caused by vertical contacts, the analytic signal is used to estimate depth using a simple amplitude half‐width rule. Two examples are shown of the application of the method. In the first example, the analytic signal highlights a circular feature beneath Lake Huron that has been identified as a possible impact crater. The second example illustrates the continuation of terranes across the Cabot Strait between Cape Breton and Newfoundland in eastern Canada.