Lineament interpretation. Short review and methodology

The ground comprises the solid and continuous surface of the Earth. The crystalline crust, i.e. bedrock, is exposed or covered with sediments and vegetation. The morphology of the ground surface is influenced by a combination of tectonometamorphic- magmatic processes (building up) and denudation/erosion processes (tearing down). Landforms are related to these processes and the character of the bedrock (lithologies and structures), and the distribution of soil or other unconsolidated, superficial material. By using remote-sensing techniques applied for structural analysis of the ground surface, it is possible to map features in the terrain that are related to bedrock structures provided that the topography of the bedrock surface is not totally concealed below a cover of soil or other loose material. Even though the sedimentary cover is relatively thick it may be distorted and the ground surface displaced by late faulting in the basement rock. Studies of the relation between structures in the bedrock and the topography started more than 150 years ago. Hobbs (1903, 1912) introduced the fundamental concept of 'lineaments' and described them as 'significant lines in the Earth's face' and later he concluded that they are 'lines in the landscape which reveal the hidden architecture of the basement'. When airborne geophysical measurements started approximately fifty years ago such data were used to compliment the topographical interpretation of basement structures. Source data for studies of lineaments consist of information on the topography (e.g. topographical maps, aerial photos, elevation data, multi-spectral sensing, laser, radar and thermography) and geophysical data (e.g. airborne geophysical data comprising magnetic, electromagnetic, radiation measurements, and gravimetric measurements). The outcome of a lineament study depends on the terrain in the investigated area, the source data, the approach and systematic performance in the interpretation, and the skill of the interpreter. Images and digital terrain models that display the relief of the studied area should, if possible, be illuminated in at least four directions to reduce biases regarding the orientation of structures. The resolution in the source data should be fully used and extrapolation of structures avoided in the primary interpretation of the source data. The interpretation of lineaments should be made in steps: a. Interpretation of each data set/image/terrain model is conducted separately; b. Compilation of all interpretations in a base lineament map and classification of the lineaments; and c. Construction of thematical maps, e.g. structural maps, rock block maps, and statistic presentation of lineaments. Generalisations and extrapolations of lineaments/structures may be made when producing the thematical maps. The construction of thematical maps should be supported by auxiliary information (geological and geomorphologic data and information on human impact in the area). Inferred tectonic structures should be controlled in field.