I think that this is the best way to do it.
- Create two grids: one with NaN and another with 0 for the bathymetry.
- I made a 2D map with the NaN grid.
- Finally, I drape the map from step 2 over the relief with 0.
Full script:
DOMAIN_volc=-R-61.7713244711/-61.5554875289/15.9359105289/16.1517474711
gmt grdcut @earth_relief_01s ${DOMAIN_volc} -Gisland.nc
gmt grdclip island.nc -Gisland_NaN.nc -Sb0/NaN -Sr0/NaN
gmt grdclip island.nc -Gtopo_island.nc -Sb0/0
gmt begin q png
gmt makecpt -Coleron -T0/2000 -M --COLOR_NAN=lightblue
gmt grdimage island_NaN.nc -C
gmt end
gmt grdview topo_island.nc -Gq.png -Bf -JM10c -JZ1c -Qc -p135/20 -png q_drape