Geophysical Modelling
Many techniques and methods have been developed for estimating depths of geological bodies. While certain methods are used to solve simple shaped anomalies, others may be required for complex anomalies. Most complicated geological structures can be represented by a combination of simple geometrical models such as edge, dyke, thin sheet, pipe, cylinder, sphere and dipole bodies. However, some magnetic or gravity anomalies are caused by geological sources that cannot be represented using simple models and should be dealt with using more complicated models such as a frustum model or as a polygon body along strike. These complicated bodies can also be treated as an ensemble statistical model for applying spectral analysis method.
In general, the depth estimation techniques can be divided into two categories: forward modelling and inversion method, or a combination of the two techniques. The forward modelling method computes the model data (profile or grid) from designed models; then uses the model data to match the target anomaly and further determine the body depth. The inversion method works in reverse relative to the forward method. It estimates the source parameters from the observed survey data. Most techniques used for depth estimations are inversion and can be classed as semi-automatic or automatic depth estimations, spectral analysis, and other methods.
There are many different techniques used to estimate source depth from magnetic field data. All automated and semi-automated methods derive depth from the curvature of the field with reference to the curvature produced by a reference model of idealised geometric shape. Some of these methods are claimed to be independent of model assumptions, but there are invariably conversion factors (often termed ‘structural indices’) that are effectively references to specific geometric shapes. The most common automated and semi-automated depth estimation methods are Werner and Euler deconvolution, and Naudy technique.
Summary of depth estimation techniques
A variety of depth estimation techniques are indicated in the table to the right. FrOG Tech routinely uses many of these techniques including forward modelling, inversion, spectral analysis and automatic depth estimation technique for our project work. The most reliable technique for depth estimation is a combination of forward modelling and inversion by using Encom ModelVision Pro™ software.
Geophysical modelling techniques offered by FrOG Tech
- Forward Modelling
- Inversion Method
- Spectral Analysis
- Semi-Automatic Depth Estimation (Automag)