[CIG-SHORT] Dynamic rupture on realistic mesh

[Huihui Weng]

Hi Brad,

When I try to simulate dynamic rupture with realistic mesh, I have a similar problem with the one Hongfeng asked several years ago. But in my case, the normal stress is large enough to hold the fault (attached pictures). 

For test, I let the dip shear stress at one node reaching the fault strength, but I find it also has slips at both normal and strike directions (as the attached pictures show, information at left bottom), i.e., dip slip ~ 0.05m, strike slip ~ 0.005m, normal slip ~ 8e-5m (fault open with normal stress large enough!). The simulating progress of this case will freeze at some time step without any errors, and the freezing time step depends on the parameter of zero_tolerance (e.g., 1.0e-7). Once the progress freezes, I need to kill it by hand by Linux commands. 

Since only the dip shear stress and normal stress are not zeros in this case, how could it lead to strike and normal slip? It does seem it is the abnormal normal slip that “freezes" the simulating progress. How can eliminate the slip at the normal direction for such realistic fault? Thanks.

Best,
Huihui


[CIG-SHORT] dynamic rupture on realistic mesh

Brad Aagaard baagaard at usgs.gov  <mailto:cig-short%40geodynamics.org?Subject=%5BCIG-SHORT%5D%20dynamic%20rupture%20on%20realistic%20mesh&In-Reply-To=4F7F6512.3050800%40whoi.edu>
Sat Apr 7 20:34:17 PDT 2012

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Hongfeng,

There are a number of potential differences between planar and nonplanar 
geometry when you setup the problem. As I mentioned before, one of the 
main differences can occur if you resolve a regional stress field onto 
nonplanar geometry. Alternatively, if you explicitly specify shear and 
normal stresses that are independent of fault orientation (e.g., a 
nominal, uniform value), then rupture is much more similar to a planar 
fault-- only the dynamic stress interaction is different.

PyLith doesn't not make any assumptions about the geometry of the fault, 
so the code works exactly the same independent of the fault geometry. 
You should examine your initial conditions and parameters to see 
precisely what the differences are between your planar and nonplanar 
models. You may want to plot the ratio of the shear strain energy to the 
fracture energy (see Steve Day's 1982 paper or Aagaard and Heaton 2008), 
which is related to how easily ruptures propagate for given set of 
conditions (stress field and friction parameters).

Regards,
Brad


On 4/6/12 2:50 PM, Hongfeng Yang wrote:
> I am running dynamic rupture scenarios on a realistic geometry mesh.
> Pylith reads in the initial stress on the fault fine--I can see the
> nucleation zone as I assigned. But in the output, slip on fault is 0,
> indicating the rupture failed to initiate.
>
> I have tried the same parameters on planar faults, one single fault
> plane and kinked fault with multiple planes. In all planar fault cases,
> rupture initiates and propagates.
>
> So it seems to relate to the mesh. Anyone has successful experience of
> running dynamic ruptures using pylith on realistic geometry fault models?
>
> Thanks,
>
> Hongfeng
>
> --
> Postdoctoral Investigator
> Department of Geology and Geophysics
> Woods Hole Oceanographic Institution
> 360 Woods Hole Rd, MS 24
> Woods Hole, MA 02543
>
>
>
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