Applying Sxy pressure to the most bottom layer of a multi-layer medium

[hosein9112400382]

Hi,

I am trying to set up a 2D model with multiple Earth layers in SPECFEM2D. I want to apply a stress of type Sxy at the bottom of the model (the lowest layer). Specifically, the stress should act along the x-direction and propagate vertically through the model.

I am wondering how to modify the source files (or other relevant input files) to apply this Sxy stress to all nodes in the bottom layer.

I guess I should use absorbing boundary conditions for the right, left, and bottom boundaries of the medium, and a fixed boundary condition for the top boundary.
However, I don't know how to apply the pressure...

Could someone guide me on which file(s) and parameters need to be changed in order to implement this type of boundary/source condition?

Thanks in advance!