# Cavities in subsurface model

**URL:** <https://community.geodynamics.org/t/cavities-in-subsurface-model/4374>\
**Category:** SW4\
**Created:** [December 2, 2025, 2:23pm UTC](https://community.geodynamics.org/t/cavities-in-subsurface-model/4374 "2025-12-02T14:23:56Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![ilabaro](https://avatars.discourse-cdn.com/v4/letter/i/5f9b8f/32.png) [@ilabaro](https://community.geodynamics.org/u/ilabaro)\
**Post date:** [December 2, 2025, 2:23pm UTC](https://community.geodynamics.org/t/cavities-in-subsurface-model/4374/1 "2025-12-02T14:23:56Z")

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Dear all,

I am trying to build a subsurface model containing a void space (cavity). I have tried to use the “block” command to add a rectangular cavity and set Vs = 0 and a very low density (1.2 kg/m3), but this makes my simulation crashing. I have also tried with Vs, Vp, density, Qs and Qp equal to -999, but this also doesn’t work. How should I proceed? Is there an alternative command to “block” that I should use?

Thanks in advance