GMT geological symbols

What’s this?

This is a collection of geological symbols for the Generic Mapping Tools (GMT) software. The symbols comprises the most widely symbols used in geological mapping for bedding, cleavage, foliation, joints and lineations. The collection currently comprises 25 symbols, being most of them dynamic, using parameters given as variables in columns of the input data. The details of the parameters used for each symbol are given below. Author of the symbols: José A. Álvarez-Gómez (jaag@ucm.es). I greatly appreciate your suggestions and feedback. These symbols are freely available under a GNU Library General Public License (version 3, or later).

How to use the symbols?

The symbols represent basically the orientation of a plane or a line in the space. For the plane the parameters used are the strike in Right Hand Rule (RHR) convention and the dip. The strike can be defined as the trend of a horizontal line on an inclined plane. It is marked by the line of intersection with a horizontal plane. The RHR establishes that the measured angle is clockwise from the north (azimuth) of the line of intersection between the plane and the horizontal, with the plane dipping orthogonally to the right when looking in the direction of the strike azimuth. The dip is the inclination of the steepest line on a plane and is perpendicular to the strike direction. For the lines the trend and plunge are used. The trend is measured clockwise from the north and the plunge is the angle of the line with the horizontal.

In order to use the symbols in GMT you need to use the program plot, using the custom symbol type -Sk[symbolname]/size; where symbolname is one of the short names of the geological symbols shown in the table below. In addition to the location of the symbol (x,y) given on the first two columns of the input file, you will need additional parameters for some of the symbols. You can also use as variables the size and color of the symbol as in any symbol plotted with plot. The table lists the parameters needed for each symbol; see the gallery for visual representation.

Symbol Description	Symbol Name	Parameters needed
Strike, dip direction and dip of beds	geo-plane	Strike, Dip
Horizontal beds	geo-plane_hor
Strike of vertical beds	geo-plane_vert	Strike
Strike, dip direction and dip of overturned beds	geo-plane_inv	Strike, Dip
Strike, dip direction and dip of bed with rake of lineation	geo-plane_rake	Strike, Dip, Rake
Strike and dip direction of gently dipping beds	geo-plane_gentle	Strike
Strike and dip direction of moderately dipping beds	geo-plane_medium	Strike
Strike and dip direction of steeply dipping beds	geo-plane_steep	Strike
Strike, dip direction and dip of crenulated or undulated beds	geo-plane_und	Strike, Dip
Strike, dip direction and dip of foliation	geo-foliation	Strike, Dip
Horizontal foliation	geo-foliation_hor
Strike of vertical foliation	geo-foliation_vert	Strike
Strike, dip direction and dip of cleavage	geo-cleavage	Strike, Dip
Horizontal cleavage	geo-cleavage_hor
Strike of vertical cleavage	geo-cleavage_vert	Strike
Strike, dip direction and dip of foliation 2	geo-foliation-2	Strike, Dip
Strike, dip direction and dip of foliation 3	geo-foliation-3	Strike, Dip
Strike, dip direction and dip of joints	geo-joint	Strike, Dip
Horizontal joints	geo-joint_hor
Strike of vertical joints	geo-joint_vert	Strike
Trend and plunge of lineation	geo-lineation	Trend, Plunge
Vertical lineation	geo-lineation_vert
Horizontal lineation	geo-lineation_hor	Trend
Trend and plunge of lineation 2	geo-lineation-2	Trend, Plunge
Trend and plunge of lineation 3	geo-lineation-3	Trend, Plunge

Symbols of the GMT geological symbols collection. The symbol short name is the name that should be used in plot -Sksymbolname/size. The extra parameters needed for each symbol are shown on the order that is expected for the symbol definition.