Plotting geological planes in profiles with Quantum GIS

Plotting the traces of geological planes in a vertical profile is a task that can be automated using a new tool of the qProf plugin for Quantum GIS. The geological measure projection on the section is determined as the intersection line between the geological plane and the section plane. The intersection position in the profile is considered to be the nearest point on the intersection line, within the geological plane and starting  from the geological measure. This technique can be used when dealing with monoclinal successions, with no or little folding, while it is not applicable to folded successions, where the projection should follow the hinge line of the folds (cf. Groshong, 3-D Structural Geology).

The qProf plugin, developed by myself and Marco Zanieri, is available for both the new Quantum GIS 2.0 version, and the previous one, 1.8. It can be directly installed from the plugin manager of Quantum GIS, or downloaded from the Quantum GIS plugin repository (vers. 0.2.1 for QGis 2.0 and vers. 0.2.0 for QGis 1.8) and then unzipped into the Python plugin folder for QGis (in my case, in Windows Vista and for QGis 2.0 is: C:\Users\mauro\.qgis2\python\plugins).

As an analysis example I consider the Mt. Alpi zone (Lucania, southern Apennines, Italy), made up of a Mesozoic carbonatic platform sequence, plus upper Miocene carbonatic-clastic sediments, presumably pertaining to the Apulian platform. The structure in the profile area is almost monoclinal, with some minor faults dissecting the sediments (not represented in the figure below). The geological stratification measures (dip direction, dip angle) derive from my undergraduate thesis, while the DEM is from Aster data.

First I select all the stratification measures in the point layer (in order to use all of them in the resulting section), then I launch the qProf plugin. In the 'Profile' tab, I calculate a profile by using the Aster data and a line layer representing the vertical profile trace. An important requirement for using the geological cross-section tool is that the profile line should consists of only two points, the start and end points, since the current version is not able to handle profiles with changing orientations. This is a requirement only for using the geological section tool, while for just creating topographic profiles there is no such restriction.

Afterwards I switch to the 'Geological cross-sections' tab, I set the source layer for the geological measures, as well as an id field (may be text or integer), and the fields for the dip direction (0-360°, clockwise from North) and the dip angle (0-90°) values. The selected points in the structural measure layer will be projected in the resulting profile.

A profile with the projected measure traces is created, with the height-length ratio scale automatically set to 1:1. You can see that the stratification is almost constantly dipping at low angles towards South-East (to the right in figure below) and that in the southern section (rightmost) the topographic profile and the stratification traces are almost parallel, as you would know as you ever climbed this 'pettata'.

The results can then be exported in csv or shapefile formats from the 'Export cross-section results' section. The result file will contain all relevant information, including the Id values that aid in finding the position of each source measure in the created profile.