[CIG-SHORT] trivial question

[Brad Aagaard]

Roby,

What you describe sounds correct. In order to understand this, I suggest 
drawing a sketch with both sides of the fault with left-lateral, 
reverse, and fault opening senses of motion. Then add the fault normal 
direction (pick one of the two possible directions) and then make 
along-strike direction "up cross normal" and the up-dip direction 
"normal cross along-strike". Look to see how these directions correspond 
to the motion on the two sides of the fault. Finally, pick the opposite 
fault normal direction and repeat. For one fault normal direction, you 
will need to flip the up-dip direction to have things make sense (this 
is what we do internally in PyLith).

Brad

On 1/30/13 10:15 AM, Roby Douilly wrote:
> Brad,
>
> Oh yes it was a typo. I meant one dipping north and the other one
> dipping south.
>
>> The fault normal direction is picked by how we insert the cohesive
>> cells. As a result we don't know which direction of the two possible
>> directions it will point. We pick the dip and along-strike directions
>> to give the correct sense of motion (positive left lateral and
>> positive reverse)
>
> That is how I understand it too but if you look at the screen shot
> below, the unit normal direction and the unit strike direction is the
> same for the both faults, I can't understand why the unit dip direction
> point on the opposite direction. The north dipping fault is pointing on
> the negative reverse side. Am I correct?
>
> Roby
>
>
>
>
> On Jan 30, 2013, at 12:42 PM, Brad Aagaard wrote:
>
>> Roby,
>>
>> Do you really mean both faults dip south or one dips south and the
>> other dips north?
>>
>> The fault normal direction is picked by how we insert the cohesive
>> cells. As a result we don't know which direction of the two possible
>> directions it will point. We pick the dip and along-strike directions
>> to give the correct sense of motion (positive left lateral and
>> positive reverse). This means you need to examine all three directions
>> to check the fault orientation. If you want to plot the slip and/or
>> traction vectors on the hanging wall, then you might need to flip the
>> signs of the slip and tractions so that they are plotted for the
>> hanging wall (one possible fault normal direction) and not the
>> footwall (the other possible fault normal direction).
>>
>> Regards,
>> Brad
>>
>> On 1/29/13 10:46 PM, Roby Douilly wrote:
>>> Hi Brad,
>>>
>>> I have two faults, one dipping south and the other one dipping south. In
>>> paraview, I output the dip_dir for both of them. For the south dipping
>>> fault the dip_dir is upward but for the north dipping fault the dip_dir
>>> is downward. Is it suppose to be like that? For the normal_dir and
>>> strike_dir it is the same but the difference is only for the dip_dir.
>>>
>>>
>>> Roby
>>>
>>> ---------------------------------------------------------------------------------
>>> Roby Douilly
>>> Graduate Student
>>> Department of Earth, Atmospheric, and Planetary Sciences
>>> Purdue University
>>> 550 Stadium Mall Dr.
>>> West Lafayette, IN 47907-2051
>>> rdouilly at purdue.edu <mailto:rdouilly at purdue.edu>
>>> <mailto:rdouilly at purdue.edu>
>>>
>>>
>>>
>>>
>>
>
>
>
> Roby
>
> ---------------------------------------------------------------------------------
> Roby Douilly
> Graduate Student
> Department of Earth, Atmospheric, and Planetary Sciences
> Purdue University
> 550 Stadium Mall Dr.
> West Lafayette, IN 47907-2051
> rdouilly at purdue.edu <mailto:rdouilly at purdue.edu>
>
>
>
>