International Geologiical Congress - Oslo 2008

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GHZ-11 Rock slope movements and early warning of catastrophic failure and related tsunamis

 

The 1783 Scilla (Italy) rock-avalanche: A reference case study for modeling coastal landslides and related tsunamis

 

Paolo Mazzanti, University of Rome "Sapienza" (Italy)
Alessandro Bosman, CNR-IGAG (Italy)
Francesca Bozzano, University of Rome "Sapienza" (Italy)
Francesco Latino Chiocci, University of Rome "Sapienza" (Italy)
Salvatore Martino, University of Rome "Sapienza" (Italy)
 

 

The 1783 coastal M. Pacì rock-avalanche is one of the most catastrophic natural slope failure historically documented in Italy. The landslide failure was triggered by the second main-shock (6 February) of the 1783 "Terremoto delle Calabrie" seismic sequence and produced a tsunami wave responsible for some 1500 losses in the neighbouring Marina Grande beach, very close to the M. Pacì slope. Detailed investigation and studies have been carried out in the last two years and are still ongoing both in the subaerial and in the submerged slopes. A detailed know-how of the area has been acquired and here proposed. Geomorphological, geological and geomechanical field surveys have been performed in the subaerial portion of the slope as well as geophysical data by 2D electrical tomography, seismic down-hole profile and passive seismic noise measurements; moreover a borehole was drilled inside the landslide mass and several laboratory tests have been carried out both for outcrop and borehole samples. In the submerged slope shallow and deep water sonar multibeam data have been collected and coupled with seismic sparker profiles in order to add sub-bottom information. Moreover dredgings, videos and dating have been planned. The collected data show a very complex landslide phenomenon characterized by a large (∼3•106m3) submerged detachment area at the foot of the subaerial slope (∼5•106m3) and a hummocky submarine bulge just in front of the scar with blocks as large as 0.2•106m3. All the geological, geophysical and geomechanical data collected can be regarded as constraints for performing and calibrating of numerical models of both landslide phenomenon and induced tsunami. In particular the engineering-geology model represents the main condition for the pre-failure modelling which is performed in order to evaluate possible relations between the subaerial and the submerged slopes. Moreover detailed subaerial and submerged pre- and post-failure topography, run-out distance, thickness and distribution of the deposit and geology along the path are available for the landslide propagation modelling. Furthermore historical data on run-up of tsunami wave along the coast and a detailed bathymetry of the coastal sector around the landslide represent a dataset adequate for the back-analysis of the induced tsunami.

 

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