[CIG-SHORT] Kinematic faults vs dynamic faults

[Ruel Jerry]

I'm using FaultCohesiveDyn and trying to get the same result that I would get if I imposed slip. I am getting equal but opposite tractions on the two sides of the fault, but that's different from the FaultCohesiveKin results which have the same sign on either side.


On Apr 23, 2012, at 10:58 AM, Brad Aagaard wrote:

> Ruel Jerry,
> 
> Please describe how you are applying "dynamic conditions" on the fault. 
> Are you using a Neumann or FaultCohesiveDyn object to apply the 
> tractions? The Neumann boundary condition is intended for external 
> boundaries, not interior interfaces. The FaultCohesiveDyn object is 
> intended for frictional interfaces. The db_initial_tractions property 
> can be used to impose initial tractions that will be equal and opposite 
> on the two sides of the fault. We have verified that it works for mode 
> II and mode III (shear) behavior. We have also verified that it works 
> for fault opening in cases where the opening is driven by Dirichlet BC, 
> but I will have to investigate what happens if the opening is driven by 
> initial tractions.
> 
> Regards,
> Brad
> 
> 
> 
> On 04/22/2012 06:45 AM, Ruel Jerry wrote:
>> Hi, I have what seems like a basic problem, but I can't seem to
>> figure it out. The model that I'm running includes faults at depth
>> that I would like to impose normal stresses on. When I use a
>> kinematic fault where I impose fault opening displacements I get the
>> surface displacements and the stress fields that I would expect. When
>> I try to use dynamic conditions on the same fault and I impose
>> tractions instead of displacement I expect to get similar results.
>> For some reason I get the correct stress on one side of the fault,
>> but the other side seems to have the sign of the stress reversed, and
>> this happens for modes 1,2 and 3. For example in mode 1 if I impose
>> slip, if I draw a line through the middle of the fault an look at the
>> XX stress, the stress values from left to right decrease until I
>> reach the fault then they increase symmetrically on the other side
>> back to 0 eventually. If I impose tractions the same line shows
>> stress values from left to right decrease until I reach the fault and
>> then at the interface I get a dislocation, then a positive value with
>> the same magnitude, then the stress decreases.
>> 
>> Is this supposed to be different or am I doing something wrong? It
>> seems like a sign problem somewhere, but I only used one value for
>> initial tractions  and one vale for fault opening.
>> 
>> Thanks, Ruel Jerry _______________________________________________
>> CIG-SHORT mailing list CIG-SHORT at geodynamics.org
>> http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short
>> 
> 
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