# 9.2.1. Magnetic Susceptibility:¶

## 9.2.1.1. Purpose¶

To demonstrate the basic steps for inverting TMI magnetic data using the induced magnetization assumption; i.e. no remanent magnetization. This exercise is meant to emulate a greenfield exploration project where topography and magnetic data are available. Here, we start with topography and synthetic magnetic data from the current best TKC susceptibility model.

Note

Example

• Download the demo . All files required for this example are located in the sub-folder “MagSusc”.

• Requires at least GIFtools version 2.1.3 (Oct 2017) (login required)

• Requires MAG3D v6.0

Import window

## 9.2.1.3. Step by step¶

Note

• The observed magnetic data can now be exported in GIF format.

• At least two anomalies are easily identified.

• Note the large trend in the data coming from the NE.

Mesh parameters

• Step 3: Processing

Inversion options

• Edit the options
• Panel 1: Set mesh, observed data and topography. Leave sensitivity options as default.

• Panel 2: Adjust $$\alpha$$ parameters (see figure)

• Click Apply and write files

Tip

As a general best practice, in the absence of a priori information, $$\alpha$$ values should be set such that all components of the regularization have equal weight. Based on the core mesh discretization used in this problem: $$\alpha_s = \left[\frac{1}{dx}\right]^2$$ and $$\alpha_z = \left[\frac{1}{2}\right]^2$$.

Recovered susceptibility model

• Step 4: Run the inversion

Note

Note the linear anomalies recovered on the edges of the core mesh that extend beyond the region of interest. These features are due to the regional signal captured by our survey. We can improve our result with the instructions in Step 5.

De-trended data

Note

Note the large negative lobe along the NE edge of the southern mag anomaly.

## 9.2.1.4. Synthesis¶

Data residual

• We have recovered a susceptibility model that honors the data within the target misfit.

• Considering a near-vertical inducing field, at least two features should raise some serious flags regarding the presence of remanence.

1. The kimberlite pipe appears to be plunging towards SW, and a secondary susceptible structure presents outside the region of interest and plunges to the East.

2. The data residual map shows correlated signal near the main anomaly, indicating a poor fit for the large negative anomaly.

Recovered susceptibility model