Looking for workflow on overburden/bedrock constraint for MVI inversion
ToddBallantyne
Posts: 4
in Geosoft
Is there any documentation on setting up vector voxel constraints for MVI? The help documentation mentions it, but I'm having little success finding discussions of it. I have a bedrock surface and would like to ensure that the MVI results are confined to the bedrock as can readily be done in susceptibility models. Is this possible?
When trying to build a model from the input vector voxel the constraint type no longer allows upper bound. I'm assuming then that a parameter reference model is to be used. I'm not clear how to define above and below the surface.
Todd
When trying to build a model from the input vector voxel the constraint type no longer allows upper bound. I'm assuming then that a parameter reference model is to be used. I'm not clear how to define above and below the surface.
Todd
0
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Hi @ToddBallantyne ,
The constraint for VOXI MVI needs to be defined as a vector voxel. The Constraint Type option under "Build A Model" simply loads the resulting voxel as that constraint. It does not restrict the constraints you can use for MVI.
For the case of limiting your overburden to have 0 or near 0 magnetization, you'll want to create an upper bound voxel AND a lower bound voxel (since MVI amplitude can have both positive and negative components).
So, in short here are the steps:
UPPER BOUND:
1. Use Voxel Math or the Build a Model tool to create a SCALAR voxel with a boundary given by your depthtobedrock grid. You can use your exported MESH with PADDING as the master voxel.
2. Above the bedrock the voxel cells should be equal to 0 or near 0 and positive. Below the bedrock the voxel cells should be equal to something large (effectively no upper bound) like 100.
3. This scalar voxel can then be used as all three components of the vector voxel which you can build using Voxels to Vector Voxel conversion tool. Save this vector voxel as "Upper bound".
LOWER BOUND:
1. Repeat the steps above for the scalar voxel but instead of near 0 (positive) use near 0 (negative) above the bedrock and 100 below the bedrock.
2. Use this scalar voxel as all three components of a vector voxel which you can build using Voxels to Vector Voxel conversion tools. Save this vector voxel as "Lower bound".
ADDING THE CONSTRAINTS:
Now simply load the upper and lower bound vector voxels as constraints in your MVI by rightclicking Upper Bound > Modify. Repeat for Lower bound.
Run the inversion.
Let me know how that turns out!Customer Success Manager  Geophysical Modelling1 
Thank you very much Taronish!0
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