[CIG-SHORT] RELAX: gps site output file

[Sylvain Barbot]

Dear Shannon,

The convention for the input and output of Relax is to use the coordinate
system (x1,x2,x3) where x1 is for north, x2 for east and x3 for depth -
unless mentioned otherwise. This is a right-handed coordinate system. The
.grd files have a more explicit name

000-north.grd
000-east.grd
000-up.grd

and 000-up.grd is positive for upwards displacement. So if everything is
working well values in 000-up.grd and the GPSX.txt files should have an
opposite sign. So this is not a bug!

If you want to use a positive value for upwards movement, you should
multiply the GPS output files by -1 in the vertical direction.

Best wishes,
Sylvain


2013/10/6 Shannon Graham <segraham at geology.wisc.edu>

>
> Hello,
>
> I was wondering if anyone has encountered an error in the sign of vertical
> displacements predicted for a GPS site (in the GPS.txt file) by RELAX? For
> example for a simple coseismic slip model, an Okada solution predicts
> uplift for a given point, using gmt's grd2xyz on the 000-up.grd file shows
> that RELAX predicts uplift for the given point. However, the GPS.txt file
> output by RELAX shows subsidence of the same magnitude. Horizontal offsets
> match for all three. All of the predicted coseismic offsets have been
> validated for this model with an Okada solution (compared against a grd2xyz
> on the 000-{east, north, or up}.grd files). Is the incorrect sign due to
> depths listed as positive, such that uplift would receive the opposite
> sign?
>
> Example:
> Okada                  easting                   northing     East disp
>               North disp               Vertical disp
>   -3 -6 -7.75E-03 -1.32E-02 3.46E-02 Relax grd2xyz
>   -3 -6 -0.007753871 -0.01320722 0.034613539 Relax GPS.txt
>   -3 -6 -7.75E-03 -1.32E-02 -3.46E-02
> Thank you in advance for any help and suggestions!
> Shannon Graham
>
> relax input file of reference:
> #/bin/bash
>
> # output directory based on script name.
> WDIR=test_defmod_10km_ny_dx_Jal
>
> if [ ! -e $WDIR ]; then
> echo $(basename $0): creating directory $WDIR
> mkdir $WDIR
> fi
>
> time relax --no-proj-output $* <<EOF | tee $WDIR/in.param
> # grid dimension (sx1,sx2,sx3)
> 512 512 512
> # sampling (dx1,dx2,dx3), smoothing (beta, nyquist)
> 3 3 3 0.2 5
> # origin position (x0,y0) and rotation
> 0 0 0
> # geographic origin (longitude, latitude, UTM zone, unit)
> #-147.73 61.04 6 1e3
> # observation depth (displacement and stress)
> 0 5
> # output directory
> $WDIR
> # lambda, mu, gamma (gamma = (1 - nu) rho g / mu)
> 30 30 1e-5
> # time interval, (positive time step) or (negative skip, scaling)
> 0 -1 1
> # number of observation planes
> 0
> # number of observation points
> 2
> # no name x1 (north) x2 (east) x3(depth)
> 1 G001 -6.0 -3.0 0.0
> 2 G002 -3.0 0.0 0.0
> # number of Coulomb planes
> 0
> # number of prestress interfaces
> 0
> # number of linear viscous interfaces
> 0
> # number of nonlinear viscous interfaces
> 0
> # number of fault creep interfaces
> 0
> # number of inter-seismic strike-slip segments
> 0
> # number of inter-seismic opening segments
> 0
> # number of events
> 1
> # number of coseismic shear-slip segments (ns)
> 1
> # no.     slip       xs       ys       zs  length   width strike   dip
> rake
> 01  1.0 -3.0783 3.94 20 10 10 308   30   90
> # number of tensile cracks
> 0
> # number of mogi source
> 0
> # number of surface traction
> 0
> EOF
>
>
>
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