MLOC Plotting Topography

MLOC Plotting Topography

This section deals with specifying digital elevation models that are used for plotting topography and/or bathymetry in the map-like plots produced by mloc. Map-like plots include the base plot and its derivatives (selected event plots, ellipse plots, seismicity plots), the direct calibration raypath plot, and the empirical path anomaly plot. Some aspects of this topic are dealt with in the installation section on data files stored in the tables/gmt/dem subdirectory. This covered below.

Calling

Plotting of topography is optional. To plot topography in all suitable plots the command dem1 is used with an argument that selects between the two available global DEMs, GLOBE and ETOPO1.

Color Palette

Any of the standard color palettes supplied with a GMT installation can be used for plotting topography in mloc. The default color palette is topo.cpt, set in mloc.f90. The command cptf can be used to change the color palette.

Considerations

The GLOBE model only includes topography, so if the plot area includes a significant amount of seafloor the ETOPO1 model is preferred. Also, mloc does not know how to stitch tiles together, so if the plot area crosses the boundary of a tile of the GLOBE model, ETOPO1 will be used.

High Resolution Topography

The resolution of the global DEM models is adequate for most clusters but in some cases it is desirable to be able to plot topography at higher resolution for the plots that cover a limited area (i.e., the base plot and derivatives). This can be done using the dem2 command, but it requires the user to provide the necessary grid file.

The dem2 command takes as an argument the pathname of a .grd file that will cover the area of the base plot. A convenient source for such data files is GMTSAR, from which SRTM topography (at 90 m resolution) and ASTER G-DEM topography (at 30 m) can be downloaded in GMT format. The requested region cannot exceed four degrees in latitude or longitude. To keep file size as small as possible, select a region slightly larger than the limits of the base plot.

mloc will make a temporary color palette for the high-resolution plots, based on the default color palette or one selected with the command cptf.

High-resolution grid files can be stored in the cluster directory but since they are rather large (a few tens of MB) and the same file would need to be stored for each series of runs, I prefer to store them in a special folder in tables/gmt/dem (I use tables/gmt/dem/custom).

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