large and negative values in magnetic susceptibility

EssamAboud

I converted 4 layer, at various depth, using GMSys-3D. layers at depths of -250, -500, -750, -1000 m depth.
before converting, I used magmap to calculate the apparent magnetic susceptibility for each layer to be used as lateral distribution.

I converted the output from magmap filter to be in MicroCGS for GMSys3D.

results gives me very large numbers of magnetic susceptibility. For example,

Layer (-250) as min= -831.90, Max= 940, mean 18.55, and std.dev= 73.11
Layer (-750) as min= -338340 and max= 3480625, mean= 17, and std.dev= 116327.
Layer (-1000) as min= -520669216, max= 534416672, mean = -173, and std. dev= 21512108 (attached)

is there any explanation for these large and negative numbers.

regards

Essam

GerryConnard

Is there some reason you are not using the lateral susceptibility inside GM-SYS 3D? It uses the same algorithm but is much more convenient. Plus it includes the effects of other layers in your model.

In an earlier post, I addressed the negative susceptibilities: https://geosoft.vanillaforums.com/discussion/comment/3485#Comment_3485

Hard to know about the large values without seeing the context. My guess is that it is related to the distance from the observations to the top of the layer. Too close and the inversion "blows up with ringing. Too far and it forces large values because of the upward continuation effect.

NatashaStanton

This is probably due to the remanent magnetization, associated to a reverse Earth Magnetic Field. Search about the paleomagnetic properties of rocks at your locality and try to use negative inclinations for the remanent field.