Probabilistic Tsunami Risk Assessment from Incomplete and Uncertain Historical Impact Records: Mediterranean and Connected Seas

Abstract

Tsunami risk is considered as the probability of a particular coastline being struck by a tsunami that may cause a certain level of impact (destructiveness). The impact metric of a tsunami is expressed in terms of tsunami intensity values, K, assigned on a 12-degree scale. To calculate tsunami risk we are based on the tsunami history of the region codified in tsunami catalogues. The probabilistic model adopted was used successfully for hazard assessment of earthquakes (Kijko et al. in Bull Seismol Soc Am 79:645–654, 2016) and of tsunamis (Smit et al. in Environmetrics 30:e2566, 2019) by considering seismic magnitude and tsunami height as metrics of the respective hazards. In this model, instead of hazard metrics we inserted risk metric, i.e. wave impact in terms of intensity values. The procedure allows utilization of the entire data set consisting not only from the complete (recent) part of tsunami catalogue but also from the highly incomplete and uncertain historical part of the catalogue. Risk is assessed in terms of probabilities of exceedance and return periods of certain intensity values in specific time frames. We applied the model using catalogues for the Mediterranean and connected seas. Sensitivity analysis showed that using complete data sets generally provided more realistic results than using entire data sets. Results indicated that the risk level depends on the seismicity level and not on the size of individual ocean basin. The highest tsunami risk level was found in the eastern Mediterranean (EM), with a significantly lower risk in the western Mediterranean (WM). In the Marmara Sea (MS), the tsunami risk was low, and the lowest was in the Black Sea (BS). The risk in the small Corinth Gulf (CG, Central Greece) was comparable to that of WM. The return period of damaging tsunamis (i.e. K ≥ 7) was 22 years in the entire Mediterranean basin and 31, 118, 135, 424, and 1660 years in the EM, WM, CG, MS, and BS basins, respectively.

New Observational Material about Seismic and Non-Seismic Tsunamis in Greece and Surrounding Areas from 1900 to 2023

“…Two tsunamis have been attributed to aseismic landslides. The possible generation of tsunamis by mechanisms related either to seismic or to aseismic tsunamis has been discussed several years ago [3,4,53].…”

“…First, observations about small tsunamis may help in better understanding tsunami generation mechanisms. Second, the cataloging of small tsunamis is quite useful for studying the scaling of tsunami size with important implications for the tsunami hazard and risk assessment with statistical and probabilistic methods based on incomplete and uncertain tsunami catalogs, e.g., [53,54].…”

Introduction to “Sixty Years of Modern Tsunami Science, Volume 2: Challenges”

“…In the first paper of the section, Triantafyllou et al ( 2023 ) introduce a probabilistic model, previously used for earthquake and tsunami hazard assessment, but instead of hazard, they focus on risk metrics, defined as the probability of a tsunami striking a coastline and causing a certain level of damage. As such, the impact metric is determined by tsunami intensity values, K , on a 12-degree scale.…”

Compilation of Regional Homogeneous Seismic Catalog for Identification of Tsunamigenic Zones in the Black Sea Region

“…The lack of digital and analog pen-and-paper records from tide gauge stations along the coast further limits achieving a certain accuracy of the estimated wave parameters. For this reason, recent tsunami hazard and risk assessment studies of the entire Black Sea region are usually performed with a dataset of varying quality and completeness regardless of what source they are generated from and are based on previously published data or research [9,12,16,22,24,32]. More than 20 tsunami events, established from the recorded and described historical data in the scientific literature, were mainly caused by earthquakes in the coastal zone or on land near the coastline of the Black Sea.…”

“…Several publications on historical Black Sea seismicity and tsunami catalogs report earthquakes of a magnitude greater than 7 (M ≥ 7) [8,22,32], most of which have generated tsunamis in the past. From 1650 to the present, evidence of five moderate intensity 4 ≤ K < 7 tsunamis on the 12-point tsunami intensity scale has been identified [8].…”