Wave and run-up (tsunami) reconstruction from ancient submarine-landslide in the Gulf of Naples, Italy

The aim of this paper is the study of the wave and run-up generation caused by ancient submarine landslides located in the canyon of the Naples Bay. Theoretical models for describing the generation and propagation of the water waves induced by submarine landslides have been recently proposed by Lynett and Liu (2002). The continental slope off the Naples Bay represents an excellent natural laboratory to study geological events and processes related to the development of submarine slides and their tsunamigenic potential. The geological setting of the Naples Bay has been studied in detail in the frame of research programmes of marine geological cartography of the Naples Bay (Aiello et al., 2001; Bruno et al., 2003; D'Argenio et al., 2004; Aiello et al., 2004; 2005; Ruggieri et al., 2007). Landslide generated tsunamis in the Ischia island has been recently evaluated by Zaniboni et al. (2007) in the frame of the INGV-DPC project V3 on volcanic hazard and risk assessment associated to the Ischia volcanic complex, north-west of the Gulf. The authors focussed, on the study of tsunamis generated by possible landslides from Ischia slopes. The catastrophic collapse that formed the large scar in the southern flank of the Ischia island (The Ischia Debris Avalanche; Chiocci and de Alteriis, 2006) can be considered as the upper limit for tsunamigenic failures in the Ischia island, but the repetition of such an event is very improbable. A new catalogue of Italian tsunamis (ITC) has been recently purposed by the INGV (Tinti et al., 2001; 2003) in the frame of the studies of European and Italian tsunamis. The ITC contains 67 events, covering the period from the tsunamigenic Plinian eruption of Vesuvius (79 A.C.) until today. The Gulf of Naples continental slope and outer shelf are deeply incised by two submarine canyons of kilometric extension, namely the Dohrn and Magnaghi canyons, representing the drainage system of this active volcanic area during the Late Quaternary. Detailed mapping of morphological features in the outer shelf and slope contributed to the knowledge of erosional and depositional processes related to the continental slope settngs and allowed on the geological interpretation of marine DEM of Dohrn and Magnaghi canyons recorded in the frame of CARG Project of marine geological mapping of the Naples Bay (Aiello et al., 2001; D'Argenio et al., 2004; Ruggieri et al., 2007). The north-western branch of the Dohrn canyon is affected by instability, with an incipient slump causing a broad depression, 200-300 m across, away from the canyon edge and semi-circular scours on the canyon walls with lateral coalescence and presentes a large area of instability, located westward of the north-western slope of the Banco di Fuori morpho-structural high. Significant slide scars in this submarine sector have been evidenced also by bathymetric profiles across the slope (Ruggieri et al., 2007). No slumped masses are preserved in the main thalweg, suggesting a probable activity of low-density turbidity currents during the Late Quaternary activity of the canyon. Large isolated blocks, showing average dimensions of 300x400m are present on the canyon floor and in its upper part the canyon floor is scoured by a minor meandering channel. These rounded morphologies are interpreted as relic structures, probably due to a selective erosion acting along the canyon's valley. On the contrary, the Magnaghi canyon is incised in the Late Quaternary volcanic deposits of the Ischia and Procida islands. A bathymetric profile has been constructed in correspondence to the scars involving the Dohrn western branch in order to give quantitative constraints to the numerical modelling. A detachment area, large about 415 m occurs at water depths ranging between - 250 m and - 37