Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 6 1 2006 10.5194/nhess-6-1-2006 http://www.nat-hazards-earth-syst-sci.net/6/1/2006/ http://www.nat-hazards-earth-syst-sci.net/6/1/2006/nhess-6-1-2006.html http://www.nat-hazards-earth-syst-sci.net/6/1/2006/nhess-6-1-2006.pdf 1 20 2006-01-02 Evidence of slope instability in the Southwestern Adriatic Margin D. Minisini F. Trincardi A. Asioli Istituto di Scienze del Mare, ISMAR-CNR, Via Gobetti 101, 40129 Bologna, Italy Dipartimento di Scienze della Terra e Geologico-Ambientali, Univ. di Bologna, Via Zamboni 67, 40127 Bologna, Italy Istituto di Geoscienze e Georisorse, IGG-CNR, C.so Garibaldi 37, 35137 Padova, Italy The Southwestern Adriatic Margin (SAM) shows evidence of widespread failure events that generated slide scars up to 10 km wide and extensive slide deposits with run out distances greater than 50 km. Chirp-sonar profiles, side-scan sonar mosaics, multibeam bathymetry and sediment cores document that the entire slope area underwent repeated failures along a stretch of 150 km and that mass-transport deposits, covering an area of 3320 km², are highly variable ranging from blocky slides to turbidites, and lay on the lower slope and in the basin. The SAM slope between 300–700 m is impacted by southward bottom currents shaping sediment drifts (partly affected by failure) and areas of dominant erosion of the seafloor. When slide deposits occur in areas swept by bottom currents their fresh appearence and their location at seafloor may give the misleading impression of a very young age. Seismic-stratigraphic correlation of these deposits to the basin floor, however, allow a more reliable age estimate through sediment coring of the post-slide unit. Multiple buried failed masses overlap each other in the lower slope and below the basin floor; the most widespread of these mass-transport deposits occurred during the MIS 2-glacial interval on a combined area of 2670 km². Displacements affecting Holocene deposits suggest recent failure events during or after the last phases of the last post-glacial eustatic rise. Differences in sediment accumulation rates at the base or within the sediment drifts and presence of downlap surfaces along the slope and further in the basin may provide one or multiple potential weak layers above which widespread collapses take place. Neotectonic activity and seismicity, together with the presence of a steep slope, represent additional elements conducive to sediment instability and failure along the SAM. Evidence of large areas still prone to failure provides elements of tsunamogenic hazard.