Caracterização de estruturas tectónicas activas da Região Sul de Portugal com recurso a ferramentas SIG : o caso da falha de São Marcos-Quarteira

Com este trabalho pretende-se avaliar o desempenho dos metodos de interpolação presentes nos softwares de Sistemas de Informação Geográfica para a produção de modelos superfície. São efectuadas varias simulações com diversos interpoladores, com dados geográficos da região emersa e imersa do sudeste Algarvio onde se localiza uma estrutura tectónica regional importante, a falha São Marcos-Quarteira. A partir de dados provenientes de levantamentos de sísmica de reflexão multicanal e monocanal de média resolução e efectuada uma interpretação sismostratigráfica dos perfis adquiridos. Com o método de interpolação mais eficiente produzem-se modelos de superfície que conduzem à interpretação da actividade neotectónica da falha São Marcos-Quarteira

Surveying the Alentejo continental shelf for minerals and Quaternary environmental changes: preliminary results of the MINEPLAT project survey

The tectonic uplift of South Portugal in the last 5 Million years (My) was firstly identified on the basis of morphologic criteria by Mariano Feio (1952, “The evolution of the relief of Baixo Alentejo and Algarve”, transl.). However, the assessment of continental vertical movements off Portugal and its relation with tectonics was only initiated in the 1990-ies. This work was carried out in the framework of FP6 and FP7 in the domains of Natural Hazards funded by the European Community. The swath bathymetry cartography of the southwest part of the Iberian Peninsula resulted from the effort of European and national projects, of 19 oceanographic surveys, a total of 200 ship time days executed from 2000 to 2006, involving 14 research institutions from 7 European countries. As a result of this effort together with acquisition and interpretation of thousands of km of seismic reflection profiles, the Pliocene-Quaternary uplift of the Alentejo continental margin (SW Portugal) is now widely accepted by the scientific community. This uplift has not been yet quantified but it is possible that can have contributed to erosion and deposition of metallic ores as placers in the continental shelf. This argues in favor of the potential existence of placers in the continental shelf and the need for the detailed investigation that will allow determination of ideal location for placers deposition in the past Pliocene-Quaternary (5 My). The source for metals can arguably be associated to the Iberian Pyrite Belt ores hosted in the Alentejo Paleozoic formations and to the hyper-alkaline intrusions of Sines and Monchique of Late Cretaceous age. Artificial renourishment of beaches with offshore sand has not been assessed for the Alentejo littoral, despite that the coast located to the south of the Sines segment shows high susceptibility to erosion. This has been observed on a regular basis as the beaches are frequently devoid of sand, thus jeopardizing their touristic potential. The detailed assessment of good quality sand deposits between approximately 30m and 50m below sea level aims at minimizing this problem that affects the economy of littoral of Alentejo. The MINEPLAT project (Assessment of the mineral resources potential in the continental shelf of Alentejo and of the environmental conditions caused by the tectonic uplift in the Pliocene-Quaternary) aims at assessing the existence of mineral deposits off the Alentejo. The MINEPLAT-1 geophysical survey acquired very high resolution multi-channel reflection seismics, swath bathymetry, backscatter and magnetic data in a test area. The preliminary results show: previously unknown NNW-SSE aligned magnetic anomalies, possibly corresponding to buried Late Cretaceous alkaline rocks; faults affecting recent sediments; well defined patches of sediments associated to morphologic traps. Future work will involve ground-truthing to characterize the shallow deposits.Alentejo 2020 contract ALT20-03-0145-FEDER-00001

High resolution seismic stratigraphy and Mass Transport Deposits of the proximal continental margin, offshore Quarteira, South Portugal: Preliminary Results.

More than 300 nautical miles of multichannel seismic reflection data were acquired in the scope of the ASTARTE project (Assessment Strategy and Risk Reduction for Tsunamis in Europe), off Quarteira, Algarve, South Portugal. The main goal of this very high resolution multichannel seismic survey was to obtain high-resolution images of the sedimentary record to try to discern the existence of high energy events, possibly tsunami backwash deposits associated with large magnitude earthquakes generated at the Africa-Eurasia plate boundary This seismic dataset was processed at the Instituto Português do Mar e da Atmosfera (IPMA), with the SeisSpace PROMAX Seismic Processing software. A tailor-made processing flow was applied, focusing in the removal of the seafloor multiple and in the enhancement of the superficial layers. A sparker source, using with 300 J of energy and a fire rate of 0,5 s was used onboard Xunauta, an 18 m long vessel. The preliminary seismostratigraphic interpretation of the Algarve ASTARTE seismic dataset allowed the identification of a complex sequence seismic units of progradational and agradational bodies as well as Mass Transported Deposits (MTD). The MTD package of sediments has a very complex internal structure, 20m of thickness, is apparently spatially controlled by an escarpment probably associated to past sea level low stands. The MTD covers across an area, approximately parallel to an ancient coastline, with >30 km (length) x 5 km (across).This work was developed as part of the project ASTARTE (603839 FP7) supported by the grant agreement No 603839 of the European Union’s Seventh. The Instituto Portugues do Mar e da Atmosfera acknowledges support by Landmark Graphics (SeisWorks) via the Landmark University Grant Program

Exploring the Alentejo continental shelf for minerals and Quaternary environmental changes: preliminary results of the MINEPLAT survey.

This study presents the preliminary results of MINEPLAT survey, organized by Universidade de Évora in partnership with Instituto Português do Mar e da Atmosfera (IPMA) based on an integrated analysis of geophysical data namely, ultra-high resolution seismic data (UHRS), multibeam data, backscatter data and magnetic data. The survey took place on north Alentejo continental shelf (30 to 200 meters depth) between Tróia and Sines. The interpretation and integration of the acquired data allows substantial improvement on the knowledge on the morphology and geology of the surface and subsurface of the Alentejo continental shelf towards the assessment of the mineral resources potential in the continental shelf off Alentejo and of the environmental conditions caused by the tectonic uplift in the Pliocene-Quaternary

Cataloguing Quaternary paleo-coastlines in West and Southwest Portugal. Economic, societal and geologic implications

A catalogue of paleo-coast lines in Southwest and South Portugal is presented based on direct field observation and on recent multibeam and backscatter bathymetric surveys. Above sea level, coastline classification was based on field observation of i) wave cut platforms directly associated with ii) notches and/or marine sand deposits with shell clasts, iii) speleothems interbedded with sand deposits and iv) beach rock slabs. Below sea level morphologic and archeologic criteria were used such as, i) buried cliffs under ii) prograding submarine prodeltas or littoral prisms, iii) hard rock surfaces interbedded with mobile sand deposits (possibly beach rock slabs), iv) lagoon depressions associated to coastal barriers sometimes buried by submerged river deltas and v) long wrinkled escarpments. Coastline erosive surfaces ranging from ∼30 m above present-day sea level to ∼120 m below present-day sea level were cataloged. The highest notches with beach sand and bioclasts appear to be well above Quaternary sea level high-stands within the realm of an area that is associated with Pliocene thrusting and uplift. This together with a series of close located well-preserved wave cut platforms and notches from ∼30m above sea level to ∼70 m below sea level require dating. Establishing an absolute chronology for these paleo-coastlines will contribute for understanding the different contributions from eustatic variations, littoral environments (sedimentation contributions) or vertical tectonic movements. The highly curvilinear pattern of the recently discovered paleo-coastlines in SW Portugal, between 30m to 80m below present day sea level, which mimics the present day coastline pattern, is associated with the inherited Paleozoic tectonic fabrics. These escarpments and embayments act as sand traps off the Iberian Pyrite Belt, worldwide famous for its base metals sulphide deposits. Ground truthing for characterizing these mobile deposits is in course looking for possible mineral placers. Thorough mapping of rocky outcrops is also important for habitat mapping, fisheries and diving activities in a region that is under tectonic uplift and needing artificial sand nourishment for keeping beaches attractive. This work was supported by the following projects: MINEPLAT- Assessment of the mineral resources potential in the continental shelf of Alentejo and of the environmental conditions caused by the tectonic uplift in the Pliocene-Quaternary (ALT20-03-0145-FEDER-000013), EMODnet Geology (European Marine Observation Data network, EASME/EMFF/2016/006

The Tagus River delta (off Lisbon, Portugal) as a repository of landslides. Implications on trigger mechanisms, tsunami hazard and neotectonics.

The seismic stratigraphy of the Tagus estuary ebb-tidal delta of Lisbon (Portugal) is investigated with the purpose of searching for evidences of possible sedimentary or erosive features associated with landslides or mass wasting deposits (MTD) events. A special attention was given to events that could have been triggered by large earthquakes that are known to have struck the West of Portugal and Spain in historical and pre-historical times. These earthquakes destroyed Lisbon at least twice in the last 500 years, being the 1755 Lisbon earthquake of estimated magnitude >8.5. To investigate these geological features the seismic reflection dataset used in this work consists of Chirp (Lisboa98 dataset), Sparker single channel (PACEMAKER 2011 dataset) and multichannel seismic (MCS) data (TAGUSDELTA 2013 dataset). Cross-lines of MCS data were acquired crossing the core sampling sites done in previous works. Calibration of the seismic lines width the core data led to infer that the Tagus ebb delta started its formation around 17ky BP and it consists of two main stratigraphic units, the younger of which initiated its formation at approximately 13ky BP. The lower deltaic unit contains several MTDs and/or landslides that could not be mapped with the present dataset. In the upper unit we report the existence of a landslide with 10km of length, 4.5km of width and 20m of maximum thickness that accounted for the collapse of half of the Tagus river delta front. The internal structure of the landslide varies laterally. The main different aspects are, as follows, i) the landslide can be dismembered along slope due to stretching parallel associated to differential movement along slope, ii) it can show internal discontinuities that represent mechanical detachments that separate imbricate wedges and iii) distal deposited bodies completely detached from the main landslide body. The age of the landslide is discussed; an estimated age of >8ky BP is proposed by stratigraphic correlation with existent cores in the Tagus pro-delta. The trigger mechanisms are discussed; there appears to be a correlation between large earthquakes and tsunami and onshore/offshore high energy deposits. The non-collapsed half of the delta front contains extensive shallow gas of still unknown origin and nature that was found thanks to the seismic surveys carried out in this study. Further geochemical and isotope studies are needed to investigate the origin of the gas as well as geotechnical studies are needed to investigate the rheology and stability of the delta. The stratigraphic model produced for the study area indicates subsidence of tens of meters from Pliocene times as the post-LGM deposits and possible coastal paleo-scarps fit well with the sea level curve for this interval whilst the Pliocene-Lower Quaternary appear to be tens of meters below the same curve. The estimation of the amount of subsidence needs a good chronostratigraphic control of the external continental shelf bodies

Nature and origin of gas trapped in sediments in the Tagus River ebb-delta, off Lisbon, Portugal, the TAGUSGAS project

The Tagus River ebb-delta is located near an important city center off Lisbon, Portugal. The Tagus delta hosts various kilometer scale landslides, the most important of which has been mapped and described with a presumable age of ~11 ky and 10 km in length, 4 km wide and 20 m of maximum thickness. An equivalent area of gas trapped in the sediments has also been reported (Terrinha et al., 2019). The TAGUSGAS project aims at characterizing the nature and source of the gas. A multibeam and backscatter survey was carried out recently covering an area of 44 km2. Several morphologic artifacts were found. The magnetic survey carried out simultaneously allows at discriminating the anthropogenic origin of some of these artifacts. It also allows at distinguishing gas and igneous rock sources of acoustic blanking in the seismic reflection record. The multibeam and backscatter basemap also serves as a tool to decide targets for seafloor sites for sample collection. The authors would like to acknowledge the FCT financial support through project UIDB/50019/2020 – IDL and TAGUSGAS project (PTDC/CTA-GEO/31885/2017)

The ASTARTE Paleotsunami Deposits data base – web-based references for tsunami research in the NEAM region

EU project ASTARTE aimed at developing a higher level of tsunami hazard assessment in the North-Eastern Atlantic, the Mediterranean and connected seas (NEAM) region by a combination of field work, experimental work, numerical modeling and technical development. The project was a cooperative work of 26 institutes from 16 countries and linked together the description of past tsunamigenic events, the identification and characterization of tsunami sources, the calculation of the impact of such events, and the development of adequate resilience and risks mitigation strategies (http://www.astarte-project.eu/). Within ASTARTE, a web-based database on Paleotsunami Deposits in the NEAM area was created with the purpose to be the future information repository for tsunami research in the broad region. The aim of the project is the integration of every existing official scientific reports and peer reviewed papers on this topic. The database, which archives information and detailed data crucial for tsunami modeling, will be updated on new entries every 12 months. A relational database managed by ArcGIS for Desktop 10.x software has been implemented. One of the final goals of the project is the public sharing of the archived dataset through a web-based map service that will allow visualizing, querying, analyzing, and interpreting the dataset. The interactive map service is hosted by ArcGIS Online and will deploy the cloud capabilities of the portal. Any interested users will be able to access the online GIS resources through any Internet browser or specific apps that run on desktop machines, smartphones, or tablets and will be able to use the analytical tools, key tasks, and workflows of the service. We will present the database structure (characterized by the presence of two main tables: the Site table and the Event table) and topics as well as their ArcGIS Online version. To date, a total of 151 sites and 220 tsunami evidence have been recorded within the ASTARTE database. The ASTARTE Paleotsunami Deposits database – NEAM region is now available online at the address http://arcg.is/1CWz0. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe).PublishedNew Orleans, USA5T. Modelli di pericolosità sismica e da maremot