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The precise location of the seismic source of 1755 CE Great Lisbon earthquake is still uncertain. The aim of this work is to use an onland sedimentary record in southern Portugal to test and validate seismic sources for the earthquake. To achieve this, tsunami deposit thicknesses from over 150 cores collected at Salgados in southern Portugal were compared to the results of a tsunami sediment transport model (Delft3D‐FLOW) that simulates tsunami propagation, inundation, erosion, and deposition. Five different hypothetical seismic sources were modeled with varying bed roughness coefficients to assess how well they reproduced observed patterns of tsunami deposit thicknesses and dune. Modeled and observed historical tsunami arrival times were also used to test different earthquake sources. Based on these comparisons, three modeled earthquake sources were able to reproduce the observed data, suggesting they should be regarded as somewhat more likely sources for the 1755 earthquake in contrast to four other modeled sources. The fault closest to shore (Marquês de Pombal) yielded the best correlations between model and observations.

Tsunami geoscience has evolved greatly since its seminal works in late 1980’s. Initially, tsunami deposits were merely identified in the stratigraphic record using its singularity and penetration inland. Later, especially after the 2004 and 2011 tsunami events, recognition of tsunami deposits progressed to interpretation on sediment dynamics and inundation phases based on the progressive application of different sedimentological, geochemical, paleontological and geophysical analytical techniques. Equally to other locations worldwide, tsunami deposits in Portugal were originally (early 1990’s) identified due to its geomorphological imprint or by its coarser sandy nature in muddy low-lying basins within the stratigraphic sequence of coastal sectors along the southern coast (Algarve). Many of these deposits were firstly studied in detail in terms of spatial distribution, texture and micropalaeontological composition. One aspect that was noticed was the uniqueness of the CE 1755 event in the top of the Holocene sequence. The CE 1755 tsunami is well-known for its consequences all over the Atlantic basin however its epicenter is yet to be established with certainty. In that sense, over the last decade, a multitude of analysis and new sites were studied (Salgados, Alcantarilha, Furnas, Barranco, Almargem) and contributed to shed new light on the CE 1755 and on other extreme events that impinged the Portuguese coastal fringe. For example, boulder analysis and the erosional signature in dune fields were used to model wave flow characteristics (run-up, flow velocity and flow depth). On the other hand, grain-size data and heavy mineral composition established a robust source-to-sink relationship between the CE 1755 tsunami deposits and dune sediments. Similarly, microtextural analysis corroborated these findings reaching similar conclusions. The application of geochemistry and high-resolution micropaleontological analysis brought new insights in terms of inundation extent and in the establishment of inundation phases. All these analyses contributed to a better understanding of the CE 1755 tsunami dynamic and its onshore sedimentological imprint. Very recently, state-of-art hydrodynamic and morphodynamic modelling exercises have been conducted using this unique geological database to be validated. They contribute to exclude potential generation zones and to narrow down the search for the CE 1755 epicenter.Another very innovative aspect is the recent study of the shelf area that is providing a ground-breaking opportunity to couple onshore and offshore palaeotsunami data and make inferences about the relevance of the backwash process on the depositional imprint.This work will summarize the present state-of-knowledge on the Portuguese tsunami geological record, a unique tsunami geoscience case-study in Europe. Authors acknowledge the financial support of FCT through projects UIDB/50019/2020–IDL and OnOff –PTDC/CTAGEO/28941/2017.

This study examined temporal distributions of macrobenthic communities in relation to bottom depth and specifically addressed whether variation in sedimentary dynamics affects species composition and functional structure. Sampling was carried in 2014 (February, May and September) off Tavira Island (southern Portugal). In each sampling period, three replicates of sediment samples were collected at 7, 12, 17 and 22 m deep for both macrobenthic and sediment characterisation. Distributional patterns of macrofauna communities were a function of the interaction between depth and temporal variability, influenced by a gradient in hydrodynamics and species recruitment. The duration of sediment remobilisation and the organic matter content in sediments were the main features of the shoreface sedimentary dynamics responsible for differences in macrobenthic species composition and feeding habits. At low depths (7 m), under intense hydrodynamic conditions and longer period of sediment remobilisation, sediments were characterised by slightly gravelly sand with low contents of organic matter and calcium carbonate. Macrobenthic communities inhabiting shallow depths displayed low abundance and species richness, being dominated by grazers and suspension feeders. In contrast, at the highest studied depth (22 m), subject to low sediment remobilisation, sediments were composed by gravelly sand with high contents of organic matter and calcium carbonate. This depth (22 m) was characterised by high abundances and species richness, reflecting a more stable macrobenthic community composed mainly by surface deposit feeders. According to the benthic communities, the seaward limit of significant wave effects on the seabed is around 7 m in low-energy periods and over 17 m in high hydrodynamic energy periods.

The southwest of the Iberian peninsula is, due to its border position between Africa and Europe, a key territory of major geoarchaeological interest, as well as a reservoir of biodiversity and a wildlife refuge area during the Holocene. Bioclimatic conditions have been significantly unstable during this period in the Western Mediterranean. Therefore, further studies are still required to understand how abrupt climate changes such as the 8.2 and 4.2 ka cal BP events impacted societies and environment. In November 2018 the RV Meteor cruise M-152 retrieved 19 vibracores and 4 gravity cores along the Algarve coast after mapping the bathymetry. One of these cores, GeoB23519-01, was taken 65 m below present sea level and recovered 365 cm of sediment. Four potential event layers were identified over the last 11 ka cal BP and, at least two of them, are related to tsunami deposits (ca. 4370 cal BP and AD 1755). This sedimentary archive was analysed in a multi-proxy approach, including palynological and micropalaeontological analyses, which allow characterizing palaeoenvironmental changes along the core. However, considering the characteristics of these deposits, we raise questions about how complex this palynological record is and how it mirrors some short-term events, climate dynamics, and cultural disruptions.

The precise location of the seismic source of Great Lisbon Earthquake is still uncertain. The aim of this work is to use the sedimentary record to test and validate seismic sources of the AD 1755 e...

Tese de doutoramento, Geologia (Geodinâmica Externa), Universidade de Lisboa, Faculdade de Ciências, 2017 Submitted by Amelia Janeiro (ajaneiro@reitoria.ul.pt) on 2018-10-09T15:39:51Z No. of bitstreams: 1 ulsd732233_td_Ivana_Coelho.pdf: 6149132 bytes, checksum: 334da2e05aac1a85bb81d6c5b6b80ef5 (MD5) Made available in DSpace on 2018-10-12T15:15:14Z (GMT). No. of bitstreams: 1 ulsd732233_td_Ivana_Coelho.pdf: 6149132 bytes, checksum: 334da2e05aac1a85bb81d6c5b6b80ef5 (MD5) Previous issue date: 2017 Fundação para a Ciência e a Tecnologia (FCT), SFRH/BD/77224/2011

The understanding of the sedimentary links between the beach and the continental shelf is crucial for the evaluation of the coastal sediment budget. However, the comprehension of this dynamics is still poorly understood owing greatly to the lack of direct sediment transport measurement at seasonal and longer time scales. This work aims at evaluating sediment transport just seaward of the closure depth through a sand tracer experiment coupled with wave–current monitoring and modelling. Observations were carried out over 1 year at 14 m depth over a sandy continental shelf offshore Tavira (southern Portugal). The sand tracer experiment was carried out by injecting 400 kg of fluorescent tracer followed by four sediment sampling surveys. Tracer results show a high dispersion of the tracer cloud with a net transport of low magnitude. Time-averaged alongshelf sediment transport rate was estimated in 0.61 m3/m/yr (southwestward) while the cross-shelf transport rate was estimated in 0.31 m3/m/yr (onshore). During the observational period nearbed currents were dominated by the northeastern component, thus flowing in the opposite direction of the tracer displacement. However, when wave-current bed shear stress exceeded the threshold of particle motion, nearbed currents were dominated by a southwestern component which is compatible with tracer displacement. Overall this study showed that seaward the closure depth bottom sediment dynamics is characterized by frequent remobilization but with very low net transport rates. info:eu-repo/semantics/publishedVersion