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 psxy, 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 psxy. 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 psxy -Sksymbolname/size. The extra parameters needed for each symbol are shown on the order that is expected for the symbol definition.