stereonet

A stereonet is a graphical tool used in structural geology to analyze the three-dimensional orientation of geological features. It projects orientations of planes and lines onto a two-dimensional circle, typically representing the lower hemisphere of the unit sphere. It supports qualitative and quantitative interpretation of fabric, faults, fractures, and bedding.

Two common stereographic projections are used: the equal-area Schmidt net and the equal-angle Wulff net. On these nets, a plane is represented by a great-circle trace; the pole to that plane is a point on the net. A line or direction is plotted as a point corresponding to its trend and plunge, or inferred from directional data. The net allows the spatial relationships to be visually assessed, such as intersection lines and angular relationships between planes.

Input data include strike and dip of planes, and trend and plunge of lines. The user can check for consistency with geological structures by plotting multiple features and looking for clustering, perpendicular relationships (e.g., bedding vs cleavage) or junctions. Statistical methods, often Fisher statistics, can be applied to compute mean directions and dispersion.

Applications include structural geology, tectonics, mineral exploration, and geotechnical engineering. It is used to test hypotheses about deformation, to infer stress fields, and to visualize foliation, lineation, and layering relationships. In modern practice, stereonets are produced with software tools and web-based calculators, which also support fitting circles, calculating angular deviations, and performing projections.