Treatise on the tectonic geomorphology of active faults: The significance of using a universal digital elevation model

This study presents the importance of the accuracy of six digital elevation models (DEMs), in the calculation of the geomorphic indices and the classification of an active fault in the Gulf of Corinth, Greece. Four of the DEMs used are based on public and global satellite imageries, the SRTM90, SRTM30, ASTER and ALOS. The other two are national DEMs: the Greek Cadastral DEM and the topographic maps of 1:5000. We applied in each DEM, for drainage basins oriented perpendicular to the fault, a series of geomorphic indices such as the drainage basin shape (Bs), the asymmetry factor (AF), the stream length-gradient index (SL), and the valley floor width to valley height ratio (Vf). These indices are used worldwide for fault activity classification. The indices calculated in the selected DEMs are compared with results from the Greek Cadastral DEM. Bs values range from 1.6 to 5.9 suggesting variably active basins, elongated according to Drainage Basin Form (RF) calculations. AF suggests systematic tilt down to the east or west. These three indices show high variability between different DEMs. Values of SL are relatively high close to the fault trace and range from 10 to 4500 and their visualization shows different narrow or inclusive patterns. Vf values range between 0.04 and 5.00 corresponding to an almost inactive fault when based on the SRTM 90 DEM to highly active using the Cadastral DEM. Our results suggest that the globally available ALOS products are quite accurate for the purposes of the tectonic geomorphology.