[CIG-SHORT] Time varying shear stress on a fault for time independent simulations.

[Josimar Alves da Silva]

Brad,

Thank you so much ! I decreased both the relative and the absolute solver
tolerances and now it worked fine.

thank you,
Josimar

On Thu, Feb 22, 2018 at 2:38 PM, Brad Aagaard <baagaard at usgs.gov> wrote:

> Josimar,
>
> Look at the residual values during the solve. I think this is a solver
> tolerance issue. You will probably want to reduce the relative solver
> tolerance if the solution you are getting is not accurate enough.
>
> My guess is that in the second time step you are simply picking up from
> where you left off on the solve in the first time step and getting smaller
> residuals. This is an effect of having an initial large residual in the
> elastic prestep with convergence due to a relative residual reduction and
> then starting with a smaller residual in the second time step and reducing
> it to a lower value.
>
> Regards,
> Brad
>
>
>
> On 02/22/2018 09:22 AM, Josimar Alves da Silva wrote:
>
>> Hi Brad,
>>
>> I am looking to understand one of the outputs of  a quasi-static, 3D,
>> elastic simulation that I am working. My simulations contains two faults (a
>> thrust fault and a strike slip fault, see attached file for further
>> details) that intersect. I use FaultCohesiveKin object to specify zero
>> fault slip for all times during my simulations in both faults. The goal is
>> to look at the stresses distribution along the faults. Please refer to the
>> attached file for a complete description of boundary conditions and
>> geometry of the model.
>>
>> At time step t=0, I observe that the left-lateral shear stress oscillates
>> wildly in both faults, but specially in the thrust fault. The same occurs
>> with less intensity on the up-dip shear and it does not occur with the
>> normal stress. I understand that t=0  time step is the one where PyLith
>> computes the quasi-static solution (elastic_prestep=True).
>>
>> In the next time steps (e.g. t=5 days) it seems that
>> the oscillations disappear, note that I have time independent boundary
>> conditions. I don't understand why this happens.
>>
>> I suspect that something is wrong with my definition of the up_dip
>> parameter. Currently I have up_dir=[0,1,0] but I have tried also
>> up_dir=[1,0,0] without success. See attached for my complete .cfg file.
>>
>> Would you know why the shear stress oscillates at t=0 days and why does
>> it get smooth at t=5 days ?  Would this be related to the up_dir direction
>> definition ?
>>
>> thank you in advance
>> Josimar
>>
>>
>>
>>
>>
>>
>>
>>
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