A question about stress change due to inward velocity and outward velocity

Hi. This is Sungho Lee.

I’ve tested three simple models.

These models consist of the upper crust (20 km), the lower crust (10 km) and mantle (370 km) and
have 2000 km * 2000 km * 400 km (just a box model).

These models are governed by a viscoplastic material model (dislocation only).

I’ve imposed inward velocity (1 cm) on the left and right boundaries and the other one is vice versa (outward 1 cm on left and right). Top surface is a just free surface boundary. The remaining boundaries are free slip.
The third one is free slip boundaries to all sides except to top (just doing nothing…).

I performed these three models using ASPECT in instantaneous.

Before doing my numerically simple experiment, I thought inward velocity induces compression comparing to the third one.

The result of the inward velocity model shows sxx(1.91E8 Pa), (3.88E8 Pa), szz(5.01E Pa), and pressure (3.88E8 Pa) but the third one shows sxx=syy=szz=P (2.74E8 Pa) at 10 km depth.

It means that inward velocity increases pressure but makes normal fault stress regime (szz > syy > sxx).

One the other hand, outward velocity decrease pressure but makes reverse fault stress regime (sxx > syy > szz).

These results are the complete opposite result I thought.

But one more interesting thing is that the free surface boundary is working well.
1 cm inward velocity induces 0.4 cm vertical displacement on top and 1 cm outward velocity induces.
0.4 cm in the vertical direction is the exact value as a volume displacement in incompressible.

Thanks

Sungho

Hi Sungho,

For clarification, are you obtaining these values from the `stress` or `shear_stress` post processor? I assume it is the `shear_stress`, but wanted to be sure.

Can you also attach a plot of the stress magnitudes for the extension and compression boundary condition cases?

Thanks!

John

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