GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.1 279 Worst-Case Credible Scenario Approach to Tsunami Hazard Assessment and Mapping in the Augusta-Siracusa district (Eastern Sicily, Italy) A. Armigliato, M. A. Paparo, G. Pagnoni, S. Tinti, F. Zaniboni Dipartimento di Fisica e Astronomia, Alma Mater Studiorum – Università di Bologna, Bologna, Italy The development of strategies for assessing tsunami hazard for the Italian coasts has received increasing interest in the last decade, as part of both European and national efforts and projects. In the framework of the EU-funded project called ASTARTE (“Assessment, STrategy And Risk Reduction for Tsunamis in Europe”), the portion of the eastern Sicily coastline (southern Italy) including the towns of Augusta and Siracusa has been selected as a test site for the development and testing of innovative methods for tsunami hazard assessment. The choice sounds very reasonable based on a number of facts, among which one can recall that 1) this area was hit by at least seven tsunamis in the approximate time interval from 1600 B.C. to present, the most famous being the A.D. 365, 1169, 1693 and 1908 tsunamis, 2) the district hosts one of the largest petrochemical poles in the Mediterranean, 3) Siracusa is listed among the UNESCO World Heritage Sites since 2005. Two main approaches to tsunami hazard assessment have been explored, one based on a probabilistic approach, the other on a worst-case credible scenario technique (see ASTARTE Deliverable D8.8, available at http://www.astarte-project.eu/files/astarte/documents/ deliverables/d8-8/ASTARTE%20D8%208%20-%20v0.9.4.pdf). The worst-case credible scenario approach and the ensuing results for Augusta and Siracusa will be illustrated and discussed in this presentation. The definition of credible worst-case tsunami scenarios for eastern Sicily involves suitable knowledge on: - the historical occurrence of tsunami in the area: we used the Euro-Mediterranean Tsunami Catalogue published by Maramai et al. (2014); - historical and pre-historical inundation deducible from paleotsunami investigations (see for instance De Martini et al. , 2012); - the known and potential tsunamigenic sources, in both the near- and far-field: we used information coming from earthquake catalogues (e.g. EMEC, Grünthal and Wahlström, 2012), databases of seismogenic faults (e.g. SHARE-ESDF, Basili et al. , 2013), and published papers presenting and discussing data acquired through marine geophysical surveys, with special reference to offshore eastern Sicily; - available literature on past large tsunamigenic earthquakes hitting eastern Sicily. As a result, we selected five main source areas to construct the worst credible scenarios for the application of the scenario-based approach to the tsunami hazard assessment for the Augusta-Siracusa area: - Hyblean-Malta escarpment (HM); - Messina Straits (MS); - Ionian Subduction region (IS); - Calabria Offshore domain (CO); - Western Hellenic arc (WH), subdivided into a northern and a southern part (the Cephalonia strike-slip zone representing the separation between the two domains). The selection of the faults, of their characteristics and of the earthquake magnitude intervals was made based on the published literature and of public seismogenic fault databases (mainly the SHARE-EDSF, seeBasili et al. , 2013).Overall,we selected32 faults covering thefive tsunamigenic source areas listed above. The southern part of the WH is assigned the largest credible magnitude interval (8.3 - 8.5); faults belonging to CO, HM and MS do not exceed maximum magnitudes of 7.1 - 7.4, while the sources found in correspondence with IS exhibit a larger variability, based on their position and mechanical role in the frame of the subduction zone (7.1 – 8.3).