# Maximum horizontal compressive stress to tensile stress?

**URL:** <https://community.geodynamics.org/t/maximum-horizontal-compressive-stress-to-tensile-stress/3212>\
**Category:** ASPECT\
**Created:** [December 29, 2023, 5:53pm UTC](https://community.geodynamics.org/t/maximum-horizontal-compressive-stress-to-tensile-stress/3212 "2023-12-29T17:53:51Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Liu](https://avatars.discourse-cdn.com/v4/letter/l/a88e57/32.png) [@Liu](https://community.geodynamics.org/u/Liu)\
**Post date:** [December 29, 2023, 5:53pm UTC](https://community.geodynamics.org/t/maximum-horizontal-compressive-stress-to-tensile-stress/3212/1 "2023-12-29T17:53:51Z")

</div>

Hi,

I am trying to understand the postprocessor output, maximum horizontal compressive stress. The output is a vector, the direction that is perpendicular to the compressive stress direction is extension. I want to get the horizontal tensile stress magnitude. Is the horizontal tensile stress magnitude same as the horizontal compressive stress magnitude. sigma\_c= -sigma?

Thanks,  
Xiaowen

---

<div class="post-metadata">

**Author:** ![jbnaliboff](https://avatars.discourse-cdn.com/v4/letter/j/58956e/32.png) [@jbnaliboff](https://community.geodynamics.org/u/jbnaliboff)\
**Post date:** [January 12, 2024, 9:53pm UTC](https://community.geodynamics.org/t/maximum-horizontal-compressive-stress-to-tensile-stress/3212/2 "2024-01-12T21:53:41Z")

</div>

Hi Xiaowen,

> I want to get the horizontal tensile stress magnitude. Is the horizontal tensile stress magnitude same as the horizontal compressive stress magnitude. sigma\_c= -sigma?

Yes, if the model is incompressible then the trace of the of the stress tensor should sum to 0, so that logic follows. To be sure, I would test this with a simple analytical model (ex: square geometry, outflow on sides, inflow on top/bottom to confirm. As a second check, you can also recalculate the stresses and stress directions by hand following the workflow in the [principal stress post processor](https://github.com/geodynamics/aspect/blob/main/source/postprocess/visualization/principal_stress.cc).

Cheers,  
John

---

<div class="post-metadata">

**Author:** ![jbnaliboff](https://avatars.discourse-cdn.com/v4/letter/j/58956e/32.png) [@jbnaliboff](https://community.geodynamics.org/u/jbnaliboff)\
**Post date:** [January 12, 2024, 9:55pm UTC](https://community.geodynamics.org/t/maximum-horizontal-compressive-stress-to-tensile-stress/3212/3 "2024-01-12T21:55:03Z")

</div>

Hi again Xioawen,

To add, please note this [relevant discussion](https://community.geodynamics.org/t/principal-stress-orientations-in-viscous-vs-visco-elastic-models/3161/4) regarding the principal stress post processors and elasticity.

Cheers,  
John