Geomorphologic evidence for postglacial activity of the Fella-Sava Fault, eastern Southern Alps, Italy

The eastern Southern Alps are a seismically active region. Research has been conducted to identify seismically active faults, with the sources of several catastrophic earthquakes still unknown.

In this study, we conducted a paleoseismological investigation around the Fella-Sava Fault in the trijunction of Austria, Italy, and Slovenia, within the epicentral area of the destructive 1348 earthquake (M_W 6.6-7.0). The Fella-Sava Fault is a ca. 100 km long, E-W- to WNW-ESE trending dextrally transpressive fault related to the Periadriatic fault system. Using digital elevation models (DEMs), we tried to identify direct evidence for surface rupturing earthquakes like fault scarps or offset geomorphic markers. Additionally, we put a special emphasis on sackungen. Sackungen are created by the gravitational collapse of mountain flanks, both aseismically and coseismically. Hillshades and aspect-maps derived from the DEMs proved suitable for mapping sackungen on a regional scale covering an area of ca. 1500 km².

A systematic remote sensing-based mapping of sackungen (of which several were subsequently ground-proven) in an area 15 km to both sides of the western segment of the Fella-Sava Fault revealed their clustering within 5 km on either side of the fault. The sackungen correlate neither with lithology nor valley depth. A directional analysis shows that the preferred trend of the sackungen is parallel to the Fella-Sava Fault and doesn’t correlate with the distribution of regional slope orientations. Thus, we suspect that the higher number sackungen in proximity of the Fella-Sava-Fault provides geomorphological evidence for its postglacial seismic activity, including the 1348 earthquake.