Monthly Archives: June 2012

Plate boundaries for GMT5’s psxy

GMT5‘s psxy offers a nice feature which lets the user designate fronts on a line segment basis – for example if you have a number of normal faults and subduction zone line segments in a multi-segment file, you can give each line a different symbol, depending on to which side the fault dips (left or right in line direction).

I have taken Peter Bird’s plate boundary file  and added these plotting instructions to the indivdual plate boundary line segment headers, for example:

> JF\NA by Peter Bird 1999
> -Sf0.45/3p+t+r

for the Juan de Fuca plate subducting under NorthAmerica. With the new header, psxy will now plot a triangle (+t) with a 3pt size (3p) to the right side (+r) of the front, fronts being separated by 0.45cm. And this is how it looks on a Robinson map centered on the dateline, generated with:


pscoast -Rg -JN180/22 -Dl -A5000 -V -G200 -K -Y4 > Bird_PlateBoundaries.ps
psxy -J -R PB2002_boundaries.gmt -W0.5p,red -O -Sf0.25/3p -Gred -Ba30:."Bird's 2003 Plate Boundaries" >> Bird_PlateBoundaries.ps

Plate boundaries plotted using GMT5’s psxy and fronts specified on line header segments


The file can be downloaded here (please make sure you cite Peter Bird’s paper as original source of the data!). The file is released under the same license as the original data.

Here’s the relevant snippet from the psxy man page for the use of -Sf in segment headers:

-Sf front. -Sfgap/size[+l|+r][+b+c+f+s+t][+ooffset]. Supply distance gap between symbols and symbol size.
If gap is negative, it is interpreted to mean the number of symbols along the front instead. Append +l
or BD+r) to plot symbols on the left or right side of the front [Default is centered]. Append +type to
specify which symbol to plot: box, circle, fault, slip, or triangle. [Default is fault]. Slip means
left-lateral or right-lateral strike-slip arrows (centered is not an option). Append +ooffset to offset
the first symbol from the beginning of the front by that amount [0]. Note: By placing -Sf options in the
segment header you can change the front types on a segment-by-segment basis.

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