ANALYSIS OF THE RELATIONSHIP OF AUTOMATICALLY AND MANUALLY EXTRACTED LINEAMENTS FROM DEM AND GEOLOGICALLY MAPPED TECTONIC FAULTS AROUND THE MAIN ETHIOPIAN RIFT AND THE ETHIOPIAN HIGHLANDS, ETHIOPIA
The paper deals with the functions that automatically extract lineaments from the 90 m Shuttle Radar Topographic Mission (SRTM) of Digital Elevation Model (DEM) (Consortium for Spatial Information 2014) in the software ArcGIS 10.1 and PCI Geomatica. They were performed for the Main Ethiopian Rift and the Ethiopian Highlands (transregional scale 1,060,000 km2), which are one of the tectonically most active areas in the world. The values of input parameters – the RADI (filter radius) value, GTHR (edge gradient threshold), LTHR (curve length), FTHR (line fitting error), ATHR (angular difference), and the DTHR (linked distance threshold) – and their influence on the final shape and number of lineaments are discussed. A map of automated extracted lineaments was created and compared with 1) the tectonic faults on the geological map by Geological Survey of Ethiopia (Mangesha et al. 1996) and 2) the lineaments based on visual interpretation by the author from the same data set. The predominant azimuth of lineaments is similar to the azimuth of the faults on the geological map. The comparison of lineaments by automated visualization in GIS and visual interpretation of lineaments carried out by the authors around the Jemma River Basin (regional scale 16,000 km2) proved that both sets of lineaments are of the same NE–SW azimuth, which is the orientation of the rift. However, lineaments mapping by automated visualization in GIS identifies a larger number of shorter lineaments than lineaments created by visual interpretation.