Magnetic geophysics · evidence summary
Two underground models fit one synthetic survey.
A visually convincing underground reconstruction can hide a dependence on modelling assumptions and regularization.
The research prompt
Original research prompt
create a 3D simulation of that; with real earth data
Two underground models fit the signal.
A 725-station synthetic magnetic survey over real terrain supported different recovered models. The comparison made non-uniqueness visible.
Synthetic magnetic observations and buried structures over real terrain. Fit ratios are not reconstruction-accuracy percentages.
The recorded investigation
Build and test the SimPEG capability
Laplace built a SimPEG workflow, starting with numerical checks and synthetic magnetic examples before moving to a three-dimensional terrain model.
Place an experiment on real terrain
The Mount St Helens example uses NOAA ETOPO terrain and a specified IGRF field, but its subsurface bodies and magnetic anomaly are synthetic.
Compare two valid-looking answers
A smooth and a compact inversion both fit the constructed signal while distributing susceptibility differently underground.
Explain non-uniqueness
Original figures and movies visualize what changes between the models. Review corrected a misfit-target definition and an earlier illustrative animation trace.
Where the conclusion stops
- Terrain is real; the magnetic observations and buried structures are synthetic.
- The reconstruction depends on the specified field, geometry and inversion assumptions.
- Misfit ratios measure fit relative to an assumed noise model, not the probability that the geology is correct.
- The supplied archive is a partial set of the artifact records.
The next useful test
Add an independent subsurface constraint or a differently sensitive survey to distinguish the competing models.
Selected scientific files
These files support inspection of the study. They are not a complete package of run inputs, dependencies or raw outputs. Scientific scripts are provided for reading; this website does not execute them.
- dc_validation.py · public copy
- inversion_scene.py · public copy
- mag3d.json
- mag3d.py
- mag3d_summary.csv
- msh3d.json
- msh3d.py
- simpeg_dc_validation.png
- simpeg_mag3d.png
- simpeg_msh_flythrough.mp4
- simpeg_msh_real.png
- simpeg_nonuniqueness.mp4
- validation.json
Public copy: internal compute identifiers and local environment paths were removed or generalized. Scientific values are retained. Paths may need adapting and some original run inputs are not included.
This is an editorial evidence summary of a recorded investigation, including later requests and review. The prompt animation is a presentation of saved work, not a live simulation. Human time saved was not measured.