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- On the source of the 8 May 1939 Azores earthquake - tsunami observations and numerical modellingPublication . Reis, Cláudia; Omira, Rachid; Matias, Luis; Baptista, Maria Ana Carvalho VianaOn 8 May 1939, an earthquake (Ms7.1) occurred near the Azores archipelago, with an epicentre located close to the western end of the Gloria fault. Previous studies present different epicentre locations spreading over a large area, and two different types of focal mechanisms. Given these uncertainties, the interpretation of the seismological information in a complex tectonic environment between the Gloria Fault and the Terceira Ridge is a matter of debate. The event caused a small tsunami recorded in the Azores Islands. In this study, we use the tsunami observations and tsunami numerical modelling to select the earthquake fault rupture that best fits the tsunami observations. We consider the different focal mechanism solutions, perform tsunami numerical modelling, and compute synthetic tsunami waveforms at the tide gauge locations. We find that an earthquake caused by a low-angle dipping fault with dominant strike-slip movement generates a tsunami that reproduces well the record at Ponta Delgada tide gauge. Finally, in areas where earthquakes are rare, the study of ancient earthquakes must use all information available, namely tsunami observations and mareograph data.
- Reply to comment on "Probabilistic Tsunami Hazard in the Northeast Atlantic From Near- and Far-Field Tectonic Sources'' by Fonseca (Pure and Applied Geophysics, 2016)Publication . Omira, Rachid; Matias, Luis; Baptista, Maria Ana Carvalho VianaThe recent events of the Indian Ocean 2004 and the Tohoku-Oki 2011 have brought to the fore the hazardous nature of the tsunami phenomenon. Consequently, understanding and quantifying the tsunami hazard have gained a significant interest from researchers worldwide. Traditionally, deterministic approach, based on the maximum credible event or the worst-case scenario, has been used to assess the tsunami hazard. However, the absence of a single comprehensive way to define this scenario makes the usefulness of the deterministic method limited (Geist and Lynett 2014). Probabilistic tsunami hazard assessment (PTHA), on the other hand, takes into consideration the contribution of multiple tsunamigenic sources to elaborate tsunami hazard maps. PTHA is now widely used in different tsunami-prone areas of the globe (Annaka et al. 2007; Thio et al. 2007; Sørensen et al. 2012; Yadav et al. 2013; Roshan et al. 2016). In the NE Atlantic, many efforts have been conducted in the aftermath of the Indian Ocean tsunami of 2004 to assess hazard posed by tsunamis. They mainly addressed the tsunami hazard through the deterministic approach with a particular focus on the coastal impact from the 1755-like event (Omira et al. 2010, 2011, 2013; Baptista et al. 2011). Alternatively, Omira et al. (2015) and, more recently, Omira et al. (2016) introduced the probabilistic tsunami hazard assessment in the NE Atlantic from sources of tectonic origin. We welcome the comment by Fonseca (2016) as it gives us the opportunity to better discuss the progress in the PTHA in the NE Atlantic. In his comment, Fonseca (2016) focuses on three main points: (1) the communication of the hazard; (2) the conservatism in the hazard analysis; (3) the uncertainty treatment. The reply to the comments raised by Fonseca (2016) will be addressed in the following sections.
- The making of the NEAM Tsunami Hazard Model 2018 (NEAMTHM18)Publication . Basili, Roberto; Brizuela, Beatriz; Herrero, Andre; Iqbal, Sarfraz; Lorito, Stefano; Maesano, Francesco Emanuele; Murphy, Shane; Perfetti, Paolo; Romano, Fabrizio; Scala, Antonio; SELVA, Jacopo; Taroni, Matteo; Tiberti, Mara Monica; Thio, Hong Kie; Tonini, Roberto; Volpe, Manuela; Glimsdal, Sylfest; Harbitz, Carl Bonnevie; Lovholt, Finn; Baptista, Maria Ana Carvalho Viana; Carrilho, Fernando; Matias, Luis; Omira, Rachid; Babeyko, Andrey; Hoechner, Andreas; Gurbuz, Mucahit; Pekcan, Onur; Yalciner, Ahmet; Canals, Miquel; Lastras, Galderic; Agalos, Apostolos; Papadopoulos, Gerassimos; TRIANTAFYLLOU, IOANNA; Benchekroun, Sabah; Jaouadi, Hedi Agrebi; Ben Ahmed, Samir; Bouallegue, Atef; Hamdi, Hassene; Oueslati, Foued; Amato, Alessandro; ARMIGLIATO, ALBERTO; Behrens, Joern; Davies, Gareth; Di Bucci, Daniela; Dolce, Mauro; Geist, Eric; GONZALEZ-VIDA, J.M.; Gonzalez, Mauricio; Macías, Jorge; Meletti, Carlo; Sozdinler, Ceren Ozer; Pagani, Marco; Parsons, Tom; Polet, Jascha; Power, William; Sorensen, Mathilde; Zaytsev, AndreyThe NEAM Tsunami Hazard Model 2018 (NEAMTHM18) is a probabilistic hazard model for tsunamis generated by earthquakes. It covers the coastlines of the North-eastern Atlantic, the Mediterranean, and connected seas (NEAM). NEAMTHM18 was designed as a threephase project. The first two phases were dedicated to the model development and hazard calculations, following a formalized decision-making process based on a multiple-expert protocol. The third phase was dedicated to documentation and dissemination. The hazard assessment workflow was structured in Steps and Levels. There are four Steps: Step-1) probabilistic earthquake model; Step-2) tsunami generation and modeling in deep water; Step-3) shoaling and inundation; Step-4) hazard aggregation and uncertainty quantification. Each Step includes a different number of Levels. Level-0 always describes the input data; the other Levels describe the intermediate results needed to proceed from one Step to another. Alternative datasets and models were considered in the implementation. The epistemic hazard uncertainty was quantified through an ensemble modeling technique accounting for alternative models' weights and yielding a distribution of hazard curves represented by the mean and various percentiles. Hazard curves were calculated at 2,343 Points of Interest (P01) distributed at an average spacing of -20 km. Precalculated probability maps for five maximum inundation heights (MIH) and hazard intensity maps for five average return periods (ARP) were produced from hazard curves. In the entire NEAM Region, MIHs of several meters are rare but not impossible. Considering a 2% probability of exceedance in 50 years (ARP approximate to 2,475 years), the POIs with MIH >5 m are fewer than 1% and are all in the Mediterranean on Libya, Egypt, Cyprus, and Greece coasts. In the North-East Atlantic, POIs with MIH >3 m are on the coasts of Mauritania and Gulf of Cadiz. Overall, 30% of the POIs have MIH >1 m. NEAMTHM1 8 results and documentation are available through the TSUMAPS-NEAM project website (http://www.tsumaps-neam.eu/), featuring an interactive web mapper. Although the NEAMTHM1 8 cannot substitute in-depth analyses at local scales, it represents the first action to start local and more detailed hazard and risk assessments and contributes to designing evacuation maps for tsunami early warning.