[CIG-SHORT] RELAX: gps site output file

[Shannon Graham]

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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