Tsunami risk perception in Central and Southern Italy, 2021

<p>The tsunami risk perception survey is promoted by the Tsunami Alert Centre of the National Institute of Geophysics and Volcanology, operating within the Italian System for Tsunami Alert (SiAM) with the Civil Protection Department and ISPRA, and acting as Tsunami Service Provider in the NEAMTWS.</p><p>Conducting studies on tsunami risk perception is important in order to obtain data on population’s knowledge and awareness, and understanding people’s perception of tsunami risk. These data are going to be added to those from two previous surveys on tsunami risk perception being issued in 2018 and 2020, to integrate the available knowledge on these issues and will provide publics, experts and policy makers with relevant tools to <strong>implement risk mitigation policies</strong>. </p><p>The third phase of the survey was completed in January 2021, administering a <strong>total of 4,207 questionnaires</strong> to the population living on the coastal areas of <em>Sicily, Campania, Latium and Sardinia</em>, <strong>in addition to the 1,635 interviewees</strong> considered in previous surveys.</p><p>The survey used a semi-structured questionnaire consisting of 27 items, with closed alternative questions, and four sets of Likert scale questions. The questionnaire was optimized for <em>CATI</em> administration, taking into account the need for conciseness and comprehensibility of the questions.</p><p>All the studied regions are located in the central Mediterranean basin (including central and southern Tyrrhenian Sea, Sardinian Sea, Sicily Channel), some of which are characterized by <strong>high tsunami hazard</strong>, and in some cases they have been affected by recorded tsunamis in a close or distant past. Some regions are located in areas where potential seismic tsunami sources are present, others surround waters where active volcanoes exist, both on islands (such as <em>Stromboli</em>, Vulcano) and below the sea (<em>Marsili, Palinuro</em>). </p><p>In addition, the four studied regions have a <strong>high risk exposure</strong> due to the <strong>high density of population living on</strong>, or visiting the coastal areas for tourism. In the areas where the questionnaire was administered, five highly populated regional capitals are located, including <em>Palermo, Messina, Naples, Rome and Cagliari</em>, together with other important towns (such as <em>Catania, Siracusa, Trapani, Salerno, Olbia</em> etc.). Moreover, the coastal shores involved in the survey, live of a <strong>significant tourist affluence</strong> in the summer period (and not only), with many tourist facilities and large hotels located along the coasts.</p><p>The survey's main aim is to analyze the perception of tsunami risk by the coastal population and to correlate levels of tsunami risk perception with scientific data from <em>probabilistic tsunami hazard assessment</em> (PTHA) for the considered coastal area. We will present some preliminary results of this last survey, with a comparison with the previous analyses on other regions in southern Italy.</p>

AN APPROACH FOR PROBABILISTIC TSUNAMI HAZARD ASSESSMENT AND APPLICATION TO SOUTHERN COASTAL AREAS OF CHINA

Seismic tsunami poses risks to many coast areas. Strong earthquakes in the area of Manila Trench may produce large-scale seismic tsunamis in South China Sea. This study aims to conduct PTHA (Probabilistic Tsunami Hazard Assessment) for the southern coastal areas of China. Several methods have already been developed to carry out PTHA, e.g. Geist & Parsons, (2006). However, there are multiple seismic parameters that affect the scale of seismic tsunamis, and those parameters are with strong uncertainties. For accurately assessing the tsunami hazard, a large number of scenarios are inevitably required to do the probabilistic statistical analysis. Therefore, existing methods do make some limits on seismic parameters to ensure the efficiency. In order to balance the accuracy and feasibility in PTHA, this study proposes a new approach.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/DllGeiaJBmo

FRAGILITY EVALUATION METHODOLOGY FOR TSUNAMI-BORNE DEBRIS IMPACT

In the safe design and risk assessment of structures in coastal area, it is important to consider tsunami-borne debris impact. Recently, probabilistic analysis has become the preferred form of analysis because of the large aleatory and epistemic uncertainties associated with tsunami effects, which are not captured in deterministic scenario-based assessments. By performing both a probabilistic tsunami hazard assessment (PTHA) and a tsunami fragility assessment (TFA) on structures, their annual failure frequency can be determined. The TFA involves evaluation of the response (e.g. debris impact force exerted on the structure) and the capacity of the structure to resist tsunami effects. Then, a fragility curve shows conditional damage probability of the structure for the tsunami magnitude (e.g., discrete tsunami height around the focused area). This study proposes a TFA methodology for tsunami-borne debris impact, as this has not yet been sufficiently established. Evaluation of the impact speed and impact probability of debris considering various uncertainties in the response evaluation are described in particular detail. Moreover, an assessment of a coastal industrial site was performed and fragility curves and the annual failure frequency of structures against debris impact were shown.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/es-ny8eIUfc