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

[Jiangzhi Chen]

That's good. It looks that I only need to calculate the 
left-lateral/reverse slip rate from the dot products of the global slip 
vector and the lateral/reverse direction vector.

Jiangzhi

On 10/31/2014 03:00 PM, Brad Aagaard wrote:
> On 10/31/2014 02:53 PM, Jiangzhi Chen wrote:
>> 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?
>
> Yes, if the fault normal is [nx,ny,nz], and "up" is [0,0,1], then the 
> lateral direction is up x normal (cross product) and the reverse 
> direction is normal x lateral. If the fault opening is zero, then the 
> slip is tangential to the fault surface.
>
> Regards,
> Brad
>
>> 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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