Browsing by Author "Baptista, Maria Ana Carvalho Viana"
Now showing 1 - 10 of 45
Results Per Page
Sort Options
- Boulder deposition during major tsunami eventsPublication . Costa, Pedro J. M.; Andrade, Cesar; Freitas, Maria C.; Oliveira, Maria A.; da Silva, Carlos M.; Omira, Rachid; Taborda, Rui; Baptista, Maria Ana Carvalho Viana; Dawson, Alastair G.A remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the Algarve (Portugal). The size-interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation, thus making this study of relevance to many other coasts worldwide. The spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity. The marine origin of the boulders is demonstrated by well-developed macro-bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves. The good state preservation of the fossils within the boulders indicates that abrasion duringtransport and redeposition was not significant. We envisage boulder deposition as having taken place during the Lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended-dominated transport and non-graded redeposition that excluded significant sorting by weight or boulder dimensions. We use numerical hydrodynamic modeling of tsunami (and storm) waves to test the observational data on boulder dimensions (density, size, distribution) on the most likely processes of sediment deposition. This work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction. Copyright (C) 2011 John Wiley & Sons, Ltd.
- Comparison between MUSCL and MOOD techniques in a finite volume well-balanced code to solve SWE. The Tohoku-Oki, 2011 examplePublication . Reis, C.; Figueiredo, J.; Clain, S.; Omira, R.; Baptista, Maria Ana Carvalho Viana; MIRANDA, JORGE MIGUELNumerical modelling is a fundamental tool for scenario-based evaluation of hazardous phenomena such as tsunami. Nevertheless, the numerical prediction highly depends on the tool quality and therefore the design of efficient numerical schemes that provide robust and accurate solutions still receives considerable attention. In this paper, we implement two different second-order finite volume numerical schemes deriving from an a priori or an a posteriori limitation procedure and we compare their efficiency in solving the non-conservative shallow-water equations. The numerical schemes assessed here are two variants of the a priori Monotonic Upstream-Centred Scheme for Conservation Laws (MUSCL) and the recent a posteriori multidimensional optimal order detection (MOOD) technique. We benchmark the numerical code, equipped with MUSCL and MOOD techniques, against: (1) a 1-D stationary problem with non-constant bathymetry to assess the second-order convergence of the method when a smooth analytical solution is involved; (2) a 1-D dam-break test to show its capacity to deal with irregular and discontinuous bathymetry in wet zones; and (3) using a simple 1-D analytical tsunami benchmark, single wave on a sloping beach', we show that the classical 1-D shallow-water system can be accurately solved by the second-order finite volume methods. Furthermore, we test the performance of the numerical code for the real-case tsunami of Tohoku-Oki, 2011. Through a set of 2-D numerical simulations, the 2011 tsunami records from both DART and GPS buoys are checked against the simulated results using MUSCL and MOOD. We find that the use of the MOOD technique leads to a better approximation between the numerical solutions and the observations than the MUSCL one. MOOD allows sharper shock capture and generates less numerical diffusion, suggesting it as a promising technique for solving shallow-water problems.
- Deep-water seamounts, a potential source of tsunami generated by landslides? The Hirondelle Seamount, NE AtlanticPublication . Omira, Rachid; Ramalho, Inês; Terrinha, Pedro; Baptista, Maria Ana Carvalho Viana; Batista, Luís; Zitellini, NevioSubmarine mass failures represent one of the most significant marine geo hazards. Their importance as a major contributor to tsunami generation and hazard has been recognized over the last 20–30 years. This study investigates a newly mapped submarine landslide, the South Hirondelle Landslide (SHL), and its potential to generate a tsunami and to threat the surrounding coasts. The SHL is located 150 km offshore South West Iberia, along the southern flank of the Hirondelle Seamount. Here, available swath bathymetry and one multichannel seismic profile show the presence of large, geometrically well constrained, deepwater landslide deposit of about 500 km3 and its associated scar. The failure likely occurred in one single event and according to a detailed numerical modelling of the landslide dynamics and of the resulting water propagation the mass failure generated a mega-tsunami, with significant impact along the surrounding coastal areas of Iberia and Morocco. This result strongly supports the inclusion of tsunami induced by deep-water submarine landslides in the marine geo-hazard assessment of the North East Atlantic region.
- Design of a sea-level tsunami detection network for the Gulf of CadizPublication . Omira, Rachid; Baptista, Maria Ana Carvalho Viana; Matias, L.; Miranda, Jorge Miguel; Catita, C.; Carrilho, F.; Toto, E.The devastating impact of the Sumatra tsunami of 26 December 2004, raised the question for scientists of how to forecast a tsunami threat. In 2005, the IOC-UNESCO XXIII assembly decided to implement a global tsunami warning system to cover the regions that were not yet protected, namely the Indian Ocean, the Caribbean and the North East Atlantic, the Mediterranean and connected seas (the NEAM region). Within NEAM, the Gulf of Cadiz is the more sensitive area, with an important record of devastating historical events. The objective of this paper is to present a preliminary design for a reliable tsunami detection network for the Gulf of Cadiz, based on a network of sea-level observatories. The tsunamigenic potential of this region has been revised in order to define the active tectonic structures. Tsunami hydrodynamic modeling and GIS technology have been used to identify the appropriate locations for the minimum number of sea-level stations. Results show that 3 tsunameters are required as the minimum number of stations necessary to assure an acceptable protection to the large coastal population in the Gulf of Cadiz. In addition, 29 tide gauge stations could be necessary to fully assess the effects of a tsunami along the affected coasts of Portugal, Spain and Morocco.
- Deterministic approach for multiple-source tsunami hazard assessment for Sines, PortugalPublication . Wronna, M.; Omira, Rachid; Baptista, Maria Ana Carvalho VianaIn this paper, we present a deterministic approach to tsunami hazard assessment for the city and harbour of Sines, Portugal, one of the test sites of project ASTARTE (Assessment, STrategy And Risk Reduction for Tsunamis in Europe). Sines has one of the most important deep-water ports, which has oil-bearing, petrochemical, liquid-bulk, coal, and container terminals. The port and its industrial infrastructures face the ocean southwest towards the main seismogenic sources. This work considers two different seismic zones: the Southwest Iberian Margin and the Gloria Fault. Within these two regions, we selected a total of six scenarios to assess the tsunami impact at the test site. The tsunami simulations are computed using NSWING, a Non-linear Shallow Water model wIth Nested Grids. In this study, the static effect of tides is analysed for three different tidal stages: MLLW (mean lower low water), MSL (mean sea level), and MHHW (mean higher high water). For each scenario, the tsunami hazard is described by maximum values of wave height, flow depth, drawback, maximum inundation area and run-up. Synthetic waveforms are computed at virtual tide gauges at specific locations outside and inside the harbour. The final results describe the impact at the Sines test site considering the single scenarios at mean sea level, the aggregate scenario, and the influence of the tide on the aggregate scenario. The results confirm the composite source of Horseshoe and Marques de Pombal faults as the worst-case scenario, with wave heights of over 10 m, which reach the coast approximately 22 min after the rupture. It dominates the aggregate scenario by about 60 % of the impact area at the test site, considering maximum wave height and maximum flow depth. The HSMPF scenario inundates a total area of 3.5 km2. © Author(s) 2015.
- Developing an Event-Tree Probabilistic Tsunami Inundation Model for NE Atlantic Coasts: Application to a Case StudyPublication . Omira, Rachid; Matias, Luís; Baptista, Maria Ana Carvalho VianaThis 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.
- Erratum to Identification of tsunami-induced deposits using numerical modeling and rock magnetism techniques: A study case of the 1755 Lisbon tsunami in Algarve, Portugal (vol 182, pg 187, 2010)Publication . Font, E.; Nascimento, C.; Omira, Rachid; Baptista, Maria Ana Carvalho Viana; Silva, P. F.Storm- and tsunami-deposits are generated by similar depositional mechanisms making their discrimination hard to establish using classic sedimentologic methods. Here we propose an original approach to identify tsunami-induced deposits by combining numerical simulation and rock magnetism. To test our method, we investigate the tsunami deposit of the Boca do Rio estuary generated by the 1755 earthquake in Lisbon which is well described in the literature. We first test the 1755 tsunami scenario using a numerical inundation model to provide physical parameters for the tsunami wave. Then we use concentration (MS. SIRM) and grain size (chi(ARM), ARM, B1/2, ARM/SIRM) sensitive magnetic proxies coupled with SEM microscopy to unravel the magnetic mineralogy of the tsunami-induced deposit and its associated depositional mechanisms. In order to study the connection between the tsunami deposit and the different sedimentologic units present in the estuary, magnetic data were processed by multivariate statistical analyses. Our numerical simulation show a large inundation of the estuary with flow depths varying from 0.5 to 6 m and run up of similar to 7 m. Magnetic data show a dominance of paramagnetic minerals (quartz) mixed with lesser amount of ferromagnetic minerals, namely titanomagnetite and titanohematite both of a detrital origin and reworked from the underlying units. Multivariate statistical analyses indicate a better connection between the tsunami-induced deposit and a mixture of Units C and D. All these results point to a scenario where the energy released by the tsunami wave was strong enough to overtop and erode important amount of sand from the littoral dune and mixed it with reworked materials from underlying layers at least 1 m in depth. The method tested here represents an original and promising tool to identify tsunami-induced deposits in similar embayed beach environments.
- Evaluating tsunami impact on the Gulf of Cadiz Coast (Northeast Atlantic)Publication . Omira, Rachid; Baptista, Maria Ana Carvalho Viana; Miranda, Jorge MiguelThe Gulf of Cadiz coasts are exposed to tsunamis. Emergency planning tools are now taking into account this fact, especially because a series of historical occurrences were strikingly significant, having left strong evidence behind, in the mareographic records, the geological evidence or simply the memory of the populations. The study area is a strip along the Algarve coast, south Portugal, an area known to have been heavily impacted by the 1 November 1755 event. In this study we use two different tsunami scenarios generated by the rupture of two thrust faults identified in the area, corresponding to 8.1-8.3 magnitude earthquakes. Tsunami propagation and inundation computation is performed using a non-linear shallow water code with bottom friction. Numerical modeling results are presented in terms of flow depth and current velocity with maximum values of 7 m and 8 m/s for inundation depth and flow speed, respectively. These results constitute a valuable tool for local authorities, emergency and decision planners to define the priority zones where tsunami mitigation measures must be implemented and to develop tsunami-resilient communities.
- Experimentally validated numerical models to assess tsunami hydrodynamic force on an elevated structurePublication . Reis, Cláudia; Clain, Stéphane; Figueiredo, Jorge; Barbosa, Andre R.; Baptista, Maria Ana Carvalho Viana; Lopes, MárioRecently, the North American and Japanese authorities began combining the tsunami forces with other loads in their structural design guidelines. Nonetheless, due to the infrequent nature of tsunamis, the provisions may benefit from complementary insights on the qualitative and quantitative characterization of the extreme phenomena and their interaction with coastal structures. The goal of this paper is to explore reliable and relatively accessible computational techniques to determine pressures and forces due to tsunami-like waves on elevated structures. Hydrodynamic flow quantities are simulated for the tsunami-like waves using an Eulerian scheme (Shallow Water equations solved by the Finite Volume method), a Lagrangian scheme (Navier-Stokes equations solved by the Smoothed Particle Hydrodynamics method), and a coupled Eulerian Lagrangian modeling approach. The numerical solutions are validated against experimental data acquired from an experimental campaign performed at the large wave flume of the Hinsdale Wave Research Laboratory, Oregon State University. The correlations between the experimental data and the numerical solutions highlight the advantages and disadvantages of the simulation techniques used, contributing to increase the confidence levels in their use in determining tsunami forces for use in structural assessments and design.
- Generation of N-waves in laboratoryPublication . Lima, Vania Veloso; Avilez-Valente, Paulo; Baptista, Maria Ana Carvalho Viana; MIRANDA, JORGE MIGUELIn this research work, a novel theoretical first-order formulation for the generation of N-waves in laboratory, by means of a piston-type wave-maker, is presented. The plate's trajectory, velocity and acceleration equations for the generation of tsunami N-waves in a wave flume are deduced. A set of laboratory experiments performed for the generation of leading depression N-waves in a wave basin is described. A Tadepalli-Synolakis N-wave profile is assumed and the equations for the paddle's trajectory, velocity, and acceleration and for the piston stroke and stroke period are derived and discussed in detail. Limits for the initial paddle velocity and acceleration are established. A set of experiments, devised and performed in the 28 m long wave basin of the Laboratory of Hydraulics, at the Faculty of Engineering of the University of Porto, is described. Six leading depression N-waves were selected and classified into three categories, according to their Stokes parameter. The results show that the shorter waves undergo a strong transformation, tending to a solitary wave-like pulse, followed by a trough. The longer waves show a distinct behaviour, tending to a bore-like wave exhibiting a leading trough. The generated longer waves presented the best results when compared with the expected Tadepalli-Synolakis N-wave profiles. Further investigation on the formulation of the wave velocity of the N-waves and on the behaviour of waves with higher order Stokes parameter is necessary.