Rachid Omira

Tsunami Characteristics Along the Peru–Chile Trench: Analysis of the 2015 Mw8.3 Illapel, the 2014 Mw8.2 Iquique and the 2010 Mw8.8 Maule Tsunamis in the Near-field

Tsunamis occur quite frequently following large magnitude earthquakes along the Chilean coast. Most of these earthquakes occur along the Peru–Chile Trench, one of the most seismically active subduction zones of the world. This study aims to understand better the characteristics of the tsunamis triggered along the Peru–Chile Trench. We investigate the tsunamis induced by the Mw8.3 Illapel, the Mw8.2 Iquique and the Mw8.8 Maule Chilean earthquakes that happened on September 16th, 2015, April 1st, 2014 and February 27th, 2010, respectively. The study involves the relation between the co-seismic deformation and the tsunami generation, the near-field tsunami propagation, and the spectral analysis of the recorded tsunami signals in the near-field. We compare the tsunami characteristics to highlight the possible similarities between the three events and, therefore, attempt to distinguish the specific characteristics of the tsunamis occurring along the Peru–Chile Trench. We find that these three earthquakes present faults with important extensions beneath the continent which result in the generation of tsunamis with short wavelengths, relative to the fault widths involved, and with reduced initial potential energy. In addition, the presence of the Chilean continental margin, that includes the shelf of shallow bathymetry and the continental slope, constrains the tsunami propagation and the coastal impact. All these factors contribute to a concentrated local impact but can, on the other hand, reduce the far-field tsunami effects from earthquakes along Peru–Chile Trench.

Tsunami impact and vulnerability in the harbour area of Tangier, Morocco

In this study, we assess tsunami impact and building vulnerability in the harbour area of Tangier – Morocco. Tsunami impact is evaluated through performing high-resolution inundation modelling. To assess buildings tsunami vulnerability, we use a geographic information system (GIS) multi-criteria approach based upon weight and classification factors. The methodology includes various steps: (i) identification of the most hazardous earthquake tsunamigenic sources, (ii) computation of high-resolution digital elevation model, (iii) simulation of inundation, (iv) field survey to classify buildings and defence structures and (v) application of the GIS-based model to produce final vulnerability map. Results show the potential tsunami impact and vulnerability that Tangier coast might face due to the occurrence of a large tsunami event in the region. Inundation map indicates that a coastal area of over 4.5 km2 is prone to tsunami flood with flow depths ranging from 0.5 to more than 6 m. Vulnerability map highlights different levels of expected buildings vulnerability to tsunami impact, which vary from “very high” for single-storey structures, located in the city harbour and along the sandy beach, to “low” for multi-storeys RC structures. Both inundation and vulnerability maps have important implications for decision makers and land use planning aiming to mitigate tsunami hazard in the North East Atlantic region.

The November, 1st, 1755 Tsunami in Morocco: Can Numerical Modeling Clarify the Uncertainties of Historical Reports?

© 2012 Omira et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The November, 1, 1755 Tsunami in Morocco: Can Numerical Modeling Clarify the Uncertainties of Historical Reports?

Probabilistic Tsunami Hazard Analysis: Multiple Sources and Global Applications

Applying probabilistic methods to infrequent but devastating natural events is intrinsically challenging. For tsunami analyses, a suite of geophysical assessments should be in principle evaluated because of the different causes generating tsunamis (earthquakes, landslides, volcanic activity, meteorological events, and asteroid impacts) with varying mean recurrence rates. Probabilistic Tsunami Hazard Analyses (PTHAs) are conducted in different areas of the world at global, regional, and local scales with the aim of understanding tsunami hazard to inform tsunami risk reduction activities. PTHAs enhance knowledge of the potential tsunamigenic threat by estimating the probability of exceeding specific levels of tsunami intensity metrics (e.g., run-up or maximum inundation heights) within a certain period of time (exposure time) at given locations (target sites); these estimates can be summarized in hazard maps or hazard curves. This discussion presents a broad overview of PTHA, including (i) sources and mechanisms of tsunami generation, emphasizing the variety and complexity of the tsunami sources and their generation mechanisms, (ii) developments in modeling the propagation and impact of tsunami waves, and (iii) statistical procedures for tsunami hazard estimates that include the associated epistemic and aleatoric uncertainties. Key elements in understanding the potential tsunami hazard are discussed, in light of the rapid development of PTHA methods during the last decade and the globally distributed applications, including the importance of considering multiple sources, their relative intensities, probabilities of occurrence, and uncertainties in an integrated and consistent probabilistic framework.

On the source of the 8 May 1939 Azores earthquake – tsunami observations and numerical modelling

ABSTRACT On 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.

The Gloria Transform Fault—NE Atlantic: Seismogenic and Tsunamigenic Potential

Abstract The Gloria Fault (GF) is a large transform segment of the Azores-Gibraltar fracture zone (AGFZ) marking the Eurasia-Nubia plate boundary in the NE Atlantic. We first provide an overview of the geodynamic setting of the AGFZ with a special emphasis on the GF, its structure, seismic activity, and tsunamigenic potential. We then present a quantitative assessment of the tsunamigenesis of the GF through numerical modeling of past tsunami events and associated possible scenarios. We found that despite the potential of the GF to generate high-magnitude earthquakes, the ensuing tsunami hazard remains low to moderate. This suggests a review of the tool used to forecast tsunamis (Tsunami Decision Matrix) in this specific region of the NE Atlantic.

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)

The 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.