[CIG-SHORT] Frictional behavior and imposed episodic slip on a fault

[Brad Aagaard]

Romain,

The current version of PyLith does not support mixing prescribed slip 
and spontaneous slip on the same fault. I do not know of a workaround 
for the issue of the single cell impeding slip between the two faults. 
Oliver Boyd asked for a mixed fault implementation a few years ago and I 
have some ideas on how it might be possible to extend the current 
formulation to handle this. I have not tried to flush out the details to 
see how practical it is because other features have higher priorities.

In the current version of PyLith, one possible solution would be to use 
a single fault controlled by spontaneous rupture (FaultCohesiveDyn) but 
setup the BC to facilitate episodic slip on the desired portion of the 
fault. This could be done via spatial variation in the friction model 
parameters or Dirichlet BC in the vicinity of the fault. The advantage 
of this approach is that the physics at the intersection between the 
portion with episodic slip and other portion of the fault will be 
consistent.

Brad


On 08/22/2012 07:31 PM, Romain Jolivet wrote:
> Hello Pylith users and developers,
>
> Is there a zero slip condition at the tip of a fault (FaultCohesiveKin object) and if yes, is there a way to remove this constraint?
>
> I explain my problem a little bit more. Here is a little drawing:
> #-------------------------------------------------------------------------------------------------#
> |                                                                                                                                   |
> |                                                                 Medium 1                                                |
> |                                                                                                                                   |
> |                                                                                                                                   |
> |                Fault 1                                                   Fault 2                                       |
> #--------------------------------#----------------------------------------------------------------#
> |         imposed slip                                        FaultCohesiveDyn                          |
> | (1 earthquake/100 yrs)                                                                                          |
> |                                                                                                                                    |
> |                                                                  Medium 2                                                |
> |                                                                                                                                    |
> #-------------------------------------------------------------------------------------------------#
>
> I would like to impose slip, episodically, on fault 1 and observe the behavior of fault 2, that has a frictional rheology. I apply dirichlet boundary conditions on the edges of medium 1 (towards the left) and medium 2 (towards the right), so that frictional creep occurs along Fault 2 between slip episodes.
>
> The problem right now is that the element at the junction between the two faults (the one that belongs to fault 2) does not slip. Consequently, creep does not propagate correctly in fault 2 after each event. Then there is a huge stress accumulation at the junction between the two faults (the problem might diverge at some point). One solution would be to have one fault (FaultCohesiveDyn) and to impose slip on part of its elements. Is it possible to impose episodes of slip on elements of a FaultCohesiveDyn object?
>
> I would like to know if this is possible to do with the latest PyLith version, if I need to implement my own fault module (Would it be easy/complicated/hard/a nightmare/impossible?) or if I should change the design of my problem?
>
> Thanks,
> Romain
>
> Romain Jolivet
> Postdoctoral Scholar
> Geological and Planetary Sciences
> California Institute of Technology, Pasadena, CA
> rjolivet at caltech.edu
> +1 (626) 560 6356
>
>
>
>
> _______________________________________________
> CIG-SHORT mailing list
> CIG-SHORT at geodynamics.org
> http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short
>