GEOLOGICAL CONTRIBUTION TO TSUMANI HAZARD ASSESSMENT ALONG ITALIAN COASTS

Abstract

This work aims to develop a study on the tsunami hazard in the NEAM region (North East Atlantic, Mediterranean and its connected seas region) with special emphasis to Italian coasts. In it, I present a multidisciplinary approach that may contribute to the tsunami hazard assessment. My research activity is divided into three different sections. The first part is based on the realization and compilation of a paleotsunami deposits geodatabase for the NEAM region in order to identify coasts affected by tsunami in the past and in order to obtain minimum run-up heights and minimum inundation distances. The second part of my thesis is focused on the research of new paleotsunami deposits inland with the aim of enriching the database, improving the knowledge of paleotsunami deposits and obtaining new data about minimum run-up heights and minimum inundation distances for a site or for a specific coastal area. In the third and final part I present the application of an approximated method to estimate the tsunami wave amplification from an offshore point to the shoreline to obtain run-up heights and inundation maps. This model, called “amplification factor method” aims to limit the computational burden associated with detailed numerical modeling of tsunami inundations. The paleotsunami deposits geodatabase-NEAM region provides us information about the minimum inundation distance, the minimum topographic height reached by the sea wave (run-up) and the age of the event. These data are useful to understand the tsunami size, the related sources and their recurrence. Therefore, information derived from paleotsunami deposits can be considered essential for a possible local application in terms of prevention by highlighting the tsunami wave inundation area. The research of new paleotsunami deposits inland was carried out along the eastern Sicily coasts (southern Italy). A typical tsunami layer was not found but interesting interpretations in terms of short lasting high energy events were carried out. The two sites, investigated so far by coring coupled with stratigraphical, sedimentological and micropaleontological analyses, exhibit some interesting data in terms of abrupt changes in the paleoenvironment. Since no typical tsunami related deposit was found, the environmental changes were interpreted as potentially related to earthquakes or tsunami wave(s) that produced a significant modification of the coastline, disrupting the morphologic sandy coastal barrier capable of protecting the sites, thus favoring a direct connection to the sea. Radiocarbon dating and detailed geomorphological mapping provided important information to constrain the recognized high energy events and compare chronological constraints with the age of some tsunami deposits found in the nearby areas. Finally, in this thesis an improved amplification factor method that takes into account local bathymetries is proposed (previously idealized bathymetries were used). The amplification factor procedure allowed me to identify NEAM coastal portions characterized by high amplification values, thus giving an overview of the wave amplification in the NEAM region. Moreover, this work shows that a potential relation between the distribution of some tsunami deposits and the wave amplification exists.