GRDGRADIENT problem

Hi,
I used grdcut to cut my slab grid file at the center longitude/latitude of -71.5/-15.5 and calculated downdip direction for this small grid file.

grdcut slabsurf2.grd -Gslabcut.grd -R-71.6/-71.4/-15.6/-15.4 -V
grdgradient slabcut.grd=nf/-1 -D -Gslabcutslope.grd -M


I got the following results:

-71.5813953488  -15.3986928105  278.410919189
-71.5069767442  -15.3986928105  281.828369141
-71.4325581395  -15.3986928105  272.162445068
-71.5813953488  -15.4705882353  280.723266602
-71.5069767442  -15.4705882353  274.995239258
-71.4325581395  -15.4705882353  271.680908203
-71.5813953488  -15.5424836601  264.232727051
-71.5069767442  -15.5424836601  263.536102295
-71.4325581395  -15.5424836601  262.71585083
-71.5813953488  -15.614379085   248.602783203
-71.5069767442  -15.614379085   252.213699341
-71.4325581395  -15.614379085   250.957290649

I can clearly notice in my slab map that the downdip direction should be in the range of 20-80 degree for this region. It doesn't make sense to have slab dipping in the SW, when it appears to be dipping along NE. I would really appreciate any advice.

Thanks
Abhash kumar
University of North Carolina at Chapel Hill


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