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  • 2013-11Journal article Open access Show more
  • Quantitative-spatial assessment of soil contamination in S. Francisco de Assis due to mining activity of the Panasqueira mine (Portugal)
    Publication . Silva, Eduardo Ferreira da; Ávila, Paula Freire; Salgueiro, Ana Rita; Candeias, Carla; Pereira, Henrique Garcia
    Through the years, mining and beneficiation processes produces large amounts of As-rich mine wastes laid up in huge tailings and open-air impoundments (Barroca Grande and Rio tailings) that are the main source of pollution in the surrounding area once they are exposed to the weathering conditions leading to the formation of AMD and consequently to the contamination of the surrounding environments, in particularly soils. In order to investigate the environmental contamination impact on S. Francisco de Assis (village located between the two major impoundments and tailings) agricultural soils, a geochemical survey was undertaken to assess toxic metals associations, related levels and their spatial distribution, and to identify the possible contamination sources. According to the calculated contamination factor, As and Zn have a very high contamination factor giving rise to 65.4 % of samples with a moderate to high pollution degree; 34.6 % have been classified as nil to very low pollution degree. The contamination factor spatial distribution put in evidence the fact that As, Cd, Cu, Pb, and Zn soils contents, downstream Barroca Grande tailing, are increased when compared with the local Bk soils. The mechanical dispersion, due to erosion, is the main contamination source. The chemical extraction demonstrates that the trace metals distribution and accumulation in S. Francisco de Assis soils is related to sulfides, but also to amorphous or poorly crystalline iron oxide phases. The partitioning study allowed understanding the local chemical elements mobility and precipitation processes, giving rise to the contamination dispersion model of the study area. The wind and hydrological factors are responsible for the chemical elements transport mechanisms, the water being the main transporter medium and soils as one of the possible retention media.
    2013-11Journal article Open access Show more
  • The 1909 Benavente (Portugal) earthquake : search for the source
    Publication . Cabral, João; Moniz, Catarina; Batlló, Josep; Figueiredo, P.; Carvalho, João; Matias, L.; Costa, Paula Teves; Dias, Ruben Pereira; Simão, N.
    The Lower Tagus River Valley has been affected by severe earthquakes comprising distant events, as in 1755, and local earthquakes, as in 1344, 1531, and 1909. The 1909 earthquake was located NE of Lisbon, near Benavente, causing serious damage and many losses. Mw 6.0 has been assessed for this earthquake and a reverse faulting focal mechanism solution has been calculated. Poor epicenter location, possible directivity and site effects, low fault slip rates, and the thick Cenozoic sedimentary cover make difficult correlation with regional structures. The focal mechanism indicates an ENE reverse fault as source, though it does not match any outcropping active structure suggesting that the event could have been produced by a blind thrust beneath the Cenozoic sedimentary fill. Hidden sources, inferred from seismic reflection data, are a possible NE structure linking the Vila Franca de Xira and the Azambuja faults, or the southern extension of the later. Evidence of surface rupturing is inhibited by the thick Holocene alluvial cover and the high fluvial sedimentation rate, though a slightly depressed area was identified in the Tagus alluvial plain W of Benavente which was investigated as possible geomorphic evidence of co-seismic surface deformation. A high-resolution seismic reflection profile was acquired across a 0.5 m high scarp at this site, and two trenches were opened across the scarp for paleoseismic research. Some deformation of dubious tectonic origin was found, requiring further studies.
    2013-11Journal article Open access Show more
  • A P-wave seismic reflection study of an intraplate structure : the Azambuja Fault, Portugal
    Publication . Carvalho, João; Alves, Daniela; Leote, Jaime; Ghose, Ranajit
    2013-11Conference object Open access Show more
  • Trace element characterization of Deception Island tephras : implications for the origin of magmas associated to recent volcanism
    Publication . Ferreira, Pedro Tavares; Santos, Rui; Ferro, André Mão de; Canário, João; Mota, Ana Maria
    2013-11Conference object Open access Show more
  • Trace element characterization of Deception Island tephras : implications for the origin of magmas associated to recent volcanism
    Publication . Ferreira, Pedro Tavares; Santos, Rui; Ferro, André Mão de; Canário, João; Mota, Ana Maria
    2013-11Conference object Open access Show more