[CIG-SHORT] slip orientation for a nonplanar fault surface

[Jiangzhi Chen]

Thanks for the clarification. If in global coordinates, the surface 
normal at the point on a subduction fault interface is n=[nx,ny,nz], is 
the lateral motion direction ns parallel to n×[0,0,1] and the reverse 
motion direction parallel to n×ns? And the fault opening is zero if all 
the points move tangentially?

Jiangzhi

On 10/31/2014 02:19 PM, Brad Aagaard wrote:
> Jiangzhi,
>
> All fault slip and tractions are specified (and output) in the local 
> fault coordinate system (left-lateral, reverse, and opening). If you 
> know the slip in a global XYZ coordinate frame, you will need to 
> compute the fault slip in the local coordinate system. If you have the 
> fault slip in the fault slip coordinate system (left-lateral, reverse, 
> opening) no conversion is necessary.
>
> If you need to convert from a global XYZ coordinate system, then I 
> suggest running a simulation that only initializes
>
> [pylithapp]
> initialize_only = True
>
> and request output of the fault orientation information
>
> [pylithapp.timedependent.interfaces.fault.output]
> vertex_info_fields = [strike_dir,dip_dir,normal_dir]
>
> so that PyLith will give you the local fault coordinate orientation to 
> use in the conversion.
>
> Regards,
> Brad
>
>
>
> On 10/31/2014 02:11 PM, Jiangzhi Chen wrote:
>> Hi Brad,
>>
>>      Just one small question. When specifying the fault parameters in
>> terms of lateral motion and reverse motion for a 3d nonplanar fault, are
>> the motions evaluated along the fault surface locally? To prescribe
>> left-lateral-slip and reverse-slip for a specific point on the surface,
>> I still need to calculate the strike, dip and rake angle at that point,
>> is that correct?
>>
>> Jiangzhi
>>
>> On 10/20/2014 03:57 PM, Brad Aagaard wrote:
>>> On 10/20/2014 03:55 PM, Jiangzhi Chen wrote:
>>>> Oh I understand what you mean, since the strain is not finite, the
>>>> deformation should not change the slip direction great enough, so the
>>>> prescribed slip should work.
>>>
>>> Correct.
>>>
>>> Regards,
>>> Brad
>>>
>>>> On 10/20/2014 03:50 PM, Brad Aagaard wrote:
>>>>> Jiangzhi,
>>>>>
>>>>> I don't understand why you think prescribed slip won't work for a
>>>>> kinematic fault interface?
>>>>>
>>>>> Regards,
>>>>> Brad
>>>>>
>>>>>
>>>>> On 10/20/2014 03:44 PM, Jiangzhi Chen wrote:
>>>>>> The time scale is several hundreds of years, about one earthquake
>>>>>> cycle.
>>>>>>
>>>>>> On 10/20/2014 03:34 PM, Brad Aagaard wrote:
>>>>>>> Jiangzhi,
>>>>>>>
>>>>>>> What time scale are you modeling? PyLith should be appropriate 
>>>>>>> if the
>>>>>>> problem can be solved with infinitesimal or small strains.
>>>>>>> Additionally, the fault formulation in PyLith breaks down when the
>>>>>>> offset become large enough so that the slip vector would need to be
>>>>>>> changing. We expect that a finite-strain formulation would be 
>>>>>>> needed
>>>>>>> as well for those types of problems.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Brad
>>>>>>>
>>>>>>> On 10/20/2014 03:24 PM, Jiangzhi Chen wrote:
>>>>>>>> Thanks for the quick response. The region is part of the Cascadia
>>>>>>>> subduction zone, where the Juan de Fuca plate moves northeastward
>>>>>>>> and
>>>>>>>> subducts. The aim is to understand how the subduction 
>>>>>>>> influences the
>>>>>>>> surface displacement field, and explains the geodetic
>>>>>>>> observation. The
>>>>>>>> upper slab interface is supposed to be a dynamic fault surface, 
>>>>>>>> and
>>>>>>>> the
>>>>>>>> lower interface is a kinematic surface. For now, I am using two
>>>>>>>> kinematic surface just to make the slab go under.
>>>>>>>>
>>>>>>>> Jiangzhi
>>>>>>>>
>>>>>>>> On 10/20/2014 03:08 PM, Brad Aagaard wrote:
>>>>>>>>> Jiangzhi,
>>>>>>>>>
>>>>>>>>> I don't understand what you are trying to do. What research
>>>>>>>>> question
>>>>>>>>> are you trying to answer? What do you want to learn from the
>>>>>>>>> simulation?
>>>>>>>>> What are your observations/constraints?
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Brad
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 10/20/2014 03:02 PM, Jiangzhi Chen wrote:
>>>>>>>>>> Hi everyone,
>>>>>>>>>>
>>>>>>>>>>      I am working on a subduction simulation, where the fault
>>>>>>>>>> interface
>>>>>>>>>> is nonplanar, and the subduction slab moves in northeast 
>>>>>>>>>> direction
>>>>>>>>>> at 4
>>>>>>>>>> cm/year before it meets the overriding plate. My question is how
>>>>>>>>>> I can
>>>>>>>>>> specify the kinematic fault interface. It is not appropriate to
>>>>>>>>>> use
>>>>>>>>>> predefined slip functions, because the slip rates depend on the
>>>>>>>>>> location
>>>>>>>>>> which is changing with time. Is there a way to make this 
>>>>>>>>>> work? Any
>>>>>>>>>> help
>>>>>>>>>> is appreciated.
>>>>>>>>>>
>>>>>>>>>> cheers,
>>>>>>>>>> Jiangzhi
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
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