[CIG-SHORT] slip vector question

[Brad Aagaard]

Roby,

Slip and traction vectors are output in the fault coordinate system 
(along strike, up-dip, and opening). The direction of the slip vector 
corresponds to the direction of motion on the "negative" side of the 
fault, which is defined by the origin of the fault normal vector. To 
convert to the global coordinate system, request that the fault 
orientation be included in the fault output via:

vertex_info_fields = [strike_dir,dip_dir,normal_dir]

With this information it is easy to rotate the slip or traction vector 
from the fault coordinate system to the global coordinate system. This 
is usually done in a Python script with HDF5 output or within ParaView 
using the calculator. The expression for the slip in global coordinates is::

 
(slip_X*strike_dir_X+slip_Y*dip_dir_X)*iHat+(slip_X*strike_dir_Y+slip_Y*dip_dir_Y)*jHat+(slip_X*strike_dir_Z+slip_Y*dip_dir_Z)*kHat

I have added this info to the PyLith FAQ wiki
http://www.geodynamics.org/cig/community/workinggroups/short/workarea/pylith-wiki

Brad