[CIG-SHORT] fault traction orientation

[Charles Williams]

The up_dir vector is used to allow PyLith to determine a consistent normal direction for a fault.  Generally, the default (0,0,1) works well.  I’m not sure if you can infer the sense of shear from the dip_dir vector.  PyLith uses these vectors internally to produce a consistent local coordinate system.  I’m not sure if you will consistently get vectors that point updip or downdip.  However, if you apply fault slip in the updip direction (positive slip value), you should have negative updip shear stress in the region where the slip was applied, and positive updip shear stress surrounding that area.  Is that what you’re seeing?

Brad is out of town at present, but he may be able to add some more info about the direction vectors when he returns.

Cheers,
Charles


> On 18/06/2015, at 12:12 pm, Birendra jha <bjha7333 at yahoo.com> wrote:
> 
> Hi Charles
> 
> I agree with positive tractionZ denoting tension.
> But isn't the updip direction determined by the "dip_dir" vector? So for the fault in picture, which has the given dip_dir vector, isn't positive tractionY pointing downdip? What is the purpose of dip_dir vector?
> 
> Thanks
> Birendra 
> --------------------------------------------
> On Wed, 6/17/15, Charles Williams <willic3 at gmail.com> wrote:
> 
> Subject: Re: [CIG-SHORT] fault traction orientation
> To: cig-short at geodynamics.org
> Date: Wednesday, June 17, 2015, 3:58 PM
> 
> Hi Birendra,
> 
> I’m fairly sure that
> positive traction y should mean updip shear, and positive
> traction z should be tension.  Similarly, positive traction
> x should be left-lateral shear.  Unfortunately, I don’t
> think we have a 3D example that demonstrates this, but you
> could put one together by putting in a dipping fault with no
> slip.  You can then apply BC that should give updip shear,
> and another set of BC to produce tension.  Look at the
> resulting fault stresses and see if this agrees with what I
> said.  Let us know if this works for you.
> 
> Cheers,
> Charles
> 
> 
>> 
> On 17/06/2015, at 2:29 am, Birendra jha <bjha7333 at yahoo.com>
> wrote:
>> 
>> Hi
>> 
>> I have questions on
> pylith fault traction orientations. Please open the attached
> figure. I loaded the fault info.vtk file in paraview to find
> out normal_dir and dip_dir directions. These vectors are in
> global coord system as per manual. For the fault in the
> picture, can you please answer those questions?
>> 
>> Thanks a
> lot
>> 
> Birendra<fault_tractions.png>_______________________________________________
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> 
> Charles A. Williams
> Scientist
> GNS Science
> 1 Fairway Drive, Avalon
> PO Box
> 30368
> Lower Hutt  5040
> New
> Zealand
> ph (office): 0064-4570-4566
> fax (office): 0064-4570-4600
> C.Williams at gns.cri.nz
> 
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Charles A. Williams
Scientist
GNS Science
1 Fairway Drive, Avalon
PO Box 30368
Lower Hutt  5040
New Zealand
ph (office): 0064-4570-4566
fax (office): 0064-4570-4600
C.Williams at gns.cri.nz