F. Gerardi

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 run-ups, 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.

Paleoseismic Investigation of Historical Liquefactions Along the Ionian Coast of Sicily

Eastern Sicily is an area where some of the most catastrophic earthquakes in Italian history occurred. As reported by historical sources, these earthquakes induced liquefaction phenomena. In two areas along the Ionian coast of Sicily we found liquefaction evidence in Holocene deposits. In the Minissale site (east of Mount Etna), the observed liquefaction features can be related to the 1169 and 1693 earthquakes, while in the Agnone site (south of Catania), the deformational structures can be tentatively associated to the 1542 and 1693 events. Both sites locate in areas where historical liquefaction has been observed in the past, thus confirming the actual liquefaction susceptibility/potential in this region. The evidence of repeated liquefaction events at the same site, highlights the relevance of the paleoseismic approach for modeling the recurrence time and preparing scenarios of seismic effects in eastern Sicily, where seismogenic sources are scantly defined.