# Help with 3D gravity forward modelling

**URL:** <https://simpeg.discourse.group/t/help-with-3d-gravity-forward-modelling/592>\
**Category:** Potential Fields\
**Created:** [August 1, 2024, 12:34pm UTC](https://simpeg.discourse.group/t/help-with-3d-gravity-forward-modelling/592 "2024-08-01T12:34:25Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Lorenzo](https://avatars.discourse-cdn.com/v4/letter/l/4da419/32.png) [@Lorenzo](https://simpeg.discourse.group/u/Lorenzo)\
**Post date:** [August 1, 2024, 12:34pm UTC](https://simpeg.discourse.group/t/help-with-3d-gravity-forward-modelling/592/1 "2024-08-01T12:34:25Z")

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Hi there. I’m trying to do gravity forward modelling on a large model of about 20_20_ 40 km, characterised by 2 density layers (a mantle with a crustal root and a crust), 2 sphere sources in the crust and a very simple topography defined by a 1000 m high mountain. I want to reproduce some sort of Bouguer anomaly in my data, so I set the topography density contrast to 0, but there is a strange circular positive anomaly in the predicted data that I can’t figure out. Can anyone help me improve my code? I’m a beginner with coding and Python, so please excuse my many mistakes.  
[fwd\_tree\_model.ipynb](https://simpeg.discourse.group/uploads/short-url/hQWKLt77qwcrQ1rvslQLCsNX867.ipynb) (241.4 KB)