# Question regarding subduction-2d example

**URL:** <https://community.geodynamics.org/t/question-regarding-subduction-2d-example/3431>\
**Category:** PyLith\
**Tags:** examples\
**Created:** [May 3, 2024, 2:47pm UTC](https://community.geodynamics.org/t/question-regarding-subduction-2d-example/3431 "2024-05-03T14:47:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![chongjh11](https://avatars.discourse-cdn.com/v4/letter/c/c37758/32.png) [@chongjh11](https://community.geodynamics.org/u/chongjh11)\
**Post date:** [May 3, 2024, 2:47pm UTC](https://community.geodynamics.org/t/question-regarding-subduction-2d-example/3431/1 "2024-05-03T14:47:38Z")

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Hello,

I’m currently trying to plot the displacement of the subduction-2d example (.h5 on MATLAB). I noticed that when I selected a point of the `step02_interseismic-groundsurf.h5` to plot the displacement over time, it is linear (for the entire 150 years or more). Am I missing something that I have to use the viscoelastic materials? Currently, I just ran the step02 without changing the properties of the material (.mat files). I can provide more information if needed!

Thanks!

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**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [May 3, 2024, 9:19pm UTC](https://community.geodynamics.org/t/question-regarding-subduction-2d-example/3431/2 "2024-05-03T21:19:39Z")

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The material models use the default settings (linear elastic rheologies). The spatial database file for the mantle includes viscosity but it is ignored when the material is linear elastic. To use a viscoelastic material for the mantle, all you need to do is change the mantle rheology to be a IsotropicLinearMaxwell.

```auto
mantle = pylith.materials.IsotropicLinearMaxwell

```

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**Author:** ![iclemus](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/iclemus/32/1752_2.png) [@iclemus](https://community.geodynamics.org/u/iclemus)\
**Post date:** [March 11, 2025, 5:35pm UTC](https://community.geodynamics.org/t/question-regarding-subduction-2d-example/3431/3 "2025-03-11T17:35:44Z")

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Hi Brad, I didn’t see this question posted but regarding the subduction-2D example,when using the Isotropic Linear Maxwell rheology, is it possible to implement time-dependent material properties? In step 3 of this example we’re able to prescribe a time for the creeping and earthquake to occur so I was curious if something similar can be done for material spatialdb? For example, having a spatialdb for the crust, ocean crust, or mantle from time 0 to 5 years, then for year 6 prescribe some other spatialdb (with different vp,vs,density, viscosity) and in year 7 go back to the original material spatialdb.

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<div class="post-metadata">

**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [March 11, 2025, 6:00pm UTC](https://community.geodynamics.org/t/question-regarding-subduction-2d-example/3431/4 "2025-03-11T18:00:18Z")

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We do not have a mechanism for imposing temporal variations in the material properties, such as Vp, Vs, and density. With the current implementation, only state variables change with time.

In general, imposing changes in the material properties would likely be inconsistent with the current stress/strain state, so it could generate stress concentrations and deformation without any additional loading. A more physically meaningful approach would be to create a bulk rheology that uses state variables (for example, temperature or some measure of damage) to change the material properties.