Effective layer magnetization maps—an alternative to reduction to the pole in aeromagnetic data interpretation

THEORETICAL AND PRACTICAL ISSUES IN THE GEOLOGICAL INTERPRETATION OF GRAVITY, MAGNETIC AND ELECTRIC FIELDS

Abstracts of the D. G. Uspensky International Seminar
Yekaterinburg: UGGGA. 1999. pp. 88–89.
P. S. Babayants (GNPP Aerogeofizika, Moscow)
Yu. I. Blokh (MGGA, Moscow)

As is well known, anomalies in the magnitude of the magnetic field depend substantially on the survey region, and a transformation called reduction to the pole is commonly used to reduce this influence. However, this reduction has its shortcomings. Transforming the anomalous field into effective layer magnetization maps is more effective.

An iterative procedure can uniquely determine the magnetization distribution in a layer between two specified contact surfaces, provided that the magnetization vector is everywhere aligned with the present-day field. The depth of the upper contact surface is specified either from independent data or from singular-point analysis in the integrated SINGULAR system. The lower contact surface is usually assumed to be horizontal, and its depth is also estimated using singular-point methods, although prior information can also be used to specify it. The program developed for IBM-compatible personal computers allows effective layer magnetization to be determined for datasets comprising approximately 10000 observation points.

The proposed method offers interpreters the following capabilities:
1) Simplification and unification of the geological interpretation of magnetic anomalies by eliminating differences associated with the direction of rock magnetization in different regions of the Earth.
2) Removal of complicating local magnetic anomalies of induced origin unrelated to geological structure, making weak local anomalies at the same locations easier to detect.
3) Identification of local objects with high natural remanent magnetization whose direction differs from that of the present-day geomagnetic field.
4) Detection of local objects whose upper or lower edge depths differ substantially from those specified for the layer as a whole.
The effectiveness of the proposed approach is supported by its practical application to processing aeromagnetic survey data from the Kirov Region of the Russian Federation and the equatorial part of Kalimantan Island.