Remote sensing of active tectonics in NE Italy, eastern Southern Alps

Due to the collision of the European and Adriatic plates, about 3 mm/yr of N-S convergence are accommodated in the Eastern and Southern Alps. This shortening is mainly taken up by c. E-W-trending reverse faults along the South Alpine Front and on NW-SE-trending dextral strike-slip faults in western Slovenia. Strong historical earthquakes and instrumental seismicity, however, show that some deformation also occurs in the interior of the Southern Alps. Little is known about which faults are active here. In this study we present results from a regional-scale remote sensing analysis focusing on the Bellunese and Friulian sectors of the Southern Alps in northeastern Italy. Our aim was to identify areas with relatively increased tectonic activity based on landscape features. We made use of high-resolution digital elevation models from aerial laser scanning campaigns. We downsampled the data to 5 m resolution and calculated the most widely used geomorphic indices that might indicate active tectonics: normalised steepness index, the Chi­ value, terrain ruggedness index, and stream knickpoints. The results were checked with geological data, mapped faults, and seismicity. We also conducted extensive field work to verify the results on the ground. Our results show that the application of large-scale tectonic geomorphology in this particular Alpine region is complicated by numerous factors. Small-scale variations in lithologies with variable erodibility strongly influence the analysis. The same holds true for variations in dip direction and dip angles of bedding planes; occasionally, vertical strata erroneously suggest linearly trending faults. In addition, we found that glacial features and alluvial deposits have locally overprinted the traces of known faults. Despite of these challenges, we found hints for active deformation in the landscape, in particular in the epicentral area of the 1976 Friuli earthquakes. We highlight potential pitfalls of the applied methods and discuss ways to overcome some of the problems we encountered.