ALBERT

Description: This study constitutes a preliminary assessment of probabilistic tsunami inundation in the NE Atlantic region. We developed an event-tree approach to calculate the likelihood of tsunami flood occurrence and exceedance of a specific near-shore wave height for a given exposure time. Only tsunamis of tectonic origin are considered here, taking into account local, regional, and far-field sources. The approach used here consists of an event-tree method that gathers probability models for seismic sources, tsunami numerical modeling, and statistical methods. It also includes a treatment of aleatoric uncertainties related to source location and tidal stage. Epistemic uncertainties are not addressed in this study. The methodology is applied to the coastal test-site of Sines located in the NE Atlantic coast of Portugal. We derive probabilistic high-resolution maximum wave amplitudes and flood distributions for the study test-site considering 100- and 500-year exposure times. We find that the probability that maximum wave amplitude exceeds 1 m somewhere along the Sines coasts reaches about 60 % for an exposure time of 100 years and is up to 97 % for an exposure time of 500 years. The probability of inundation occurrence (flow depth 〉0 m) varies between 10 % and 57 %, and from 20 % up to 95 % for 100- and 500-year exposure times, respectively. No validation has been performed here with historical tsunamis. This paper illustrates a methodology through a case study, which is not an operational assessment.

Description: Probabilistic Tsunami Hazard Assessment requires the existence of a synthetic earthquake catalogue obeying the geodynamic framework of the source area and a fault model for each event. Usually, we assume a constant fault displacement, eventually filtered by a simple closure condition. The distribution of events by magnitude classes follows a truncated Gutenberg-Richter law with epicentres uniformly distributed in the source domain. This approach makes that the slip on the source structures will extend beyond the generation domain being heterogeneous inside that domain. This contradicts the assumption that the slip is caused by geodynamic constraints. Here, we propose a methodology for creating synthetic earthquake catalogues and we apply it to the Gloria Fault in the Atlantic. With three instrumental tsunamis recorded: 08.05.1939, 25.11.1941 and 26.05.1975 [1]. Additionally, we propose a semi-empirical scaling law for the generation of the tsunamigenic earthquakes

Description: Highlights • Novel conceptional model for the tsunamigenesis of coastal mass-wasting events. • Unlocking the debate on the tsunamigenic potential of small-scale coastal collapses. • Benchmarking a cliff-failure tsunami numerical model with historical data. • First detailed investigation of the 1930 Cabo Girão tsunami in Madeira, NE Atlantic. Mass-wasting events are a key process in the evolution of volcanic ocean islands. They occur at various dimensional scales and present a major source of hazard. When the collapsed material plunges into the sea, destructive tsunamis can be generated. Yet, the hazard potential of collapse-induced tsunamis is still poorly understood with different opinions on what consequences to expect from this type of events, particularly those related to massive volcanic island flank collapses. In this paper, however, we explore the hazard extent of tsunamis triggered by the smaller – but more frequent – coastal cliff-failures, in order to isolate critical factors in the generation, propagation and impact of these tsunamis. To achieve this, we use the prime example of Madeira, a volcanic island in the Atlantic Ocean highly vulnerable to cliff-failure. Particularly, we explore the March 4th, 1930 Cabo Girão event that triggered a deadly tsunami. The coastal impact of the 1930 “Deadly Wave”, as the island's inhabitants referred to the generated tsunami, resulted in 19 fatalities. We use historical description, morphological analysis, and numerical modelling to better understand the tsunamigenesis of tall island cliffs failing into the sea. Interestingly, we find that a relatively small-scale mass-wasting event (∼0.003 km3 volume) was the cause of the reported tsunami that inundated the nearest coasts. Our numerical results, fairly agreeing with the available collapse and subsequent tsunami descriptions, suggest that the tsunami impact was mainly localized on the southern coast of Madeira Island. Furthermore, our study allows proposing a novel morphology-based conceptional model for the tsunamigenesis and hazard extent induced by mass-wasting events on oceanic volcanic islands.