Discrimination of Tsunami Sources (Earthquake versus Landslide) on the Basis of Historical Data in Eastern Sicily and Southern Calabria

Abstract

The source mechanisms responsible for large historical tsunamis that have struck eastern Sicily and southern Calabria are a topic of robust debate. We have compiled a database of historical coeval descriptions of three large tsunamis: 11 January 1693, 6 February 1783, and 28 December 1908. By using accounts of run-up and inundation and employing an approach proposed by Okal and Synolakis in 2004, we can provide discriminants to define the nature of the near-field tsunami sources (fault dislocation or landslide).Historical reports for the 1908 event describe affected localities, maximum runups, and inundation areas. However, for the 1693 and 1783 tsunamis, reports are limited to inundation and occasional run-up estimates. We calculate run-up values for these events using available relations between inundation and run-up. We employed the model of Okal and Synolakis to the obtained profiles of tsunami run-up along the inundated shorelines. The 1908 run-up data distribution confirms that the tsunami is compatible with a seismic dislocation source, whereas the 1783 data supports contemporary observations and recent offshore investigations suggesting that the tsunami was produced by an earthquake-triggered submarine landslide. Analysis of the 1693 event data suggests that the tsunami was generated during a tectonic event and thus a seismogenic source should be found offshore.

Active tectonics along the submarine slope of south-eastern Sicily and the source of the 11 January 1693 earthquake and tsunami

“…Nevertheless, it can be appreciated that our simulation reproduces well the one and only actual observation in Augusta. The matching is satisfactory in Siracusa, while in Catania the run-up modelled by our simulation underestimates that from Gerardi et al (2008), and the same happens, even in a more pronounced way, towards the north.…”

“…Assessing run-up values in any location is rather critical. Only two such "quantitative measurements" for the 1693 tsunami are available in Augusta, as reported in Gerardi et al (2008). In that study, the authors computed run-up values in a number of other localities by adopting the Hills and Mader (1997) relations.…”

“…6; but we have to take these comparison with caution, because in Fig. 6 we are comparing two different tsunami metrics, the maximum water elevation (resulting from our modelling) and the run-up estimated by Gerardi et al (2008). The numerical simulation of the run-up requires detailed information on the actual coastal topography in early 1693, which is not available to the authors.…”

“…Finally, and most important, no recent submarine landslides of suitable size have been found in the area north of Mount Etna (see the comments of Argnani et al, 2009b on a tsunamigenic slide supposedly located in the same position). It is also worth stressing that Gerardi et al (2008), analysing the inundation pattern of the 1693 tsunami along the Sicily coast and using a discriminatory tool introduced by Okal and Synolakis (2004) for near-shore tsunami sources, came to the conclusion that the characteristics of this tsunami were more compatible with an earthquake rather than with a landslide source. Our results support this conclusion, as we have demonstrated in this work that even a submarine landslide close to the coastal area, where the observed tsunami waves were larger, cannot reproduce the 11 January 1693 tsunami effects.…”

Calibration of a real-time tsunami detection algorithm for sites with no instrumental tsunami records: application to coastal tide-gauge stations in eastern Sicily, Italy

“…According to the Italian tsunami catalogue , most of these tsunamis are associated with large local earthquakes (e.g. 1693,1783,1908), but recently their purely tectonic origin was questioned and a debate was opened on the possible parallel or prevalent contribution provided by submarine landslides triggered by seismic shaking (see tsunami studies and tsunami source analyses in Piatanesi and Tinti, 1998;Graziani et al, 2006;Gutscher et al, 2006;Tinti et al, 2007;Papadopoulos et al, 2007;Billi et al, 2008;Gerardi et al, 2008;Favalli et al, 2009;Argnani et al, 2009Argnani et al, , 2012. Indeed, because of the morphology and steep bathymetry of the Messina Strait and of the Hyblean-Malta escarpment bordering eastern Sicily offshore, landslide excitation by earthquakes and even by simple gravitational loading cannot be ruled out, which means that landslides can be considered a further source of tsunami.…”