DSpace Collection:
http://hdl.handle.net/10174/996
2024-03-29T08:11:13ZMuografia e a sua primeira aplicação em Portugal, na Mina do Lousal
http://hdl.handle.net/10174/33415
Title: Muografia e a sua primeira aplicação em Portugal, na Mina do Lousal
Authors: Pedro, Teixeira; Alberto, Blanco; Bento, Caldeira; Bernardo, Tomé; João, Matos; José, Borges; Lorenzo, Cazon; Luis, Lopes; Luis, Afonso; Marco, Pinto; Mário, Pimenta; Mourad, Bezzeghoud; Paolo, Dobrilla; Pedro, Assis; Raul, Pereira; Rui, Oliveira; Sofia, Andringa
Abstract: A muografia é uma técnica de sondagem não invasiva que usa muões, uma radiação natural de fundo com algum poder penetrante, para observar o interior das estruturas atravessadas. Com detetores adequados à observação da subsuperfície terrestre é possível criar muografias, imagens com informação sobre a distribuição de densidades da região observada.
Internacionalmente, esta técnica já foi aplicada em várias áreas. Em Portugal, está a ser aplicada pela primeira vez na área da geofísica para fazer um reconhecimento geológico da Mina do Lousal.2022-12-01T00:00:00ZA Sismicidade de Portugal
http://hdl.handle.net/10174/24812
Title: A Sismicidade de Portugal
Authors: Bezzeghoud, Mourad; Caldeira, Bento; Borges, José F.
Abstract: Portugal can be considered to have a moderate seismicity characterized by small events (M<5.0) and occasional moderate/large/major (5.0<=M<=7.8) earthquakes. The northern and central part of Portugal are characterized by a low seismicity (M<5.0) except Lower Tejo Valley region, which exhibits the relatively high seismic activity. At least three important historical earthquakes have occurred in this zone in 1344 (Ms=6.0), 1531 (Ms=7.1) and 23 April 1909 (Mw=6.0). The southern part of Portugal is the region with the most significant seismicity and can be divided into two areas: the Atlantic adjacent zone; and the continental zone. The first one is characterized by more intense seismic activity associated with the convergence between Eurasian and African plates. The southwest of cape of São Vicente area, where the earthquakes of 28 February 1969 (Ms=8.0) and 1 November 1755 (so-called Lisbon earthquake, Io=X-XI) occurred, is probably the most seismically active zone. According to the Portugal southern mainland neotectonic map it is possible to identify the following main tectonic structures: a) the Messejana fault, with an extension of 500 km crossing all of the southern region with NE-SW orientation and which is probably associated with the Azores-Gibraltar fault; b) close to the city of Évora, the Moura-Vidigueira fault has a WNW-ESE strike; and c) the Loulé fault, located in Algarve with an approximately W-E orientation, probably responsible for large historical earthquakes. The seismic studies of the western zone of the Iberian Peninsula has revealed four zones of high seismic strain elease: the Lower Tejo Valley, the Gorringe Bank zone, the southern Algarve and the area around the city of Évora. The southern region of Portugal (mainly the Algarve) and the Lisbon region (including the Lower Tejo Valley region) are the zones that have suffered the greatest number of disastrous earthquakes.2018-01-01T00:00:00ZEstudo Geofísico e Geológico da Falha de Vila Franca de Xira
http://hdl.handle.net/10174/24792
Title: Estudo Geofísico e Geológico da Falha de Vila Franca de Xira
Authors: Carvalho, João; Alves, Daniela; Borges, José F.; Caldeira, Bento; Cabral, João; Dias, Rui; Casacão, João; Oliveira, Rui Jorge; Leote, Jaime
Abstract: A região de Lisboa e Vale Inferior do Tejo foi afetada
por vários sismos destrutivos que provocaram grandes
prejuízos materiais e perdas de vida. As fontes geradoras
desses sismos históricos situam-se quer na zona
de fronteira de placas Ibéria-África, localizada cerca
de 300 km a sul, quer no interior da própria região.
Neste artigo, estuda-se uma falha geológica local, a
falha de Vila Franca de Xira, que se julga ter ocasionado
o terramoto de Lisboa de 1531. Apesar da ausência de
evidência geológica direta para a presença duma rotura
superficial da falha, demonstra-se através da utilização
de métodos geofísicos que se trata de uma zona
de falha ativa, sendo possivelmente a fonte de geração
daquele sismo.2018-01-01T00:00:00ZThermal Structure in SPZ and Southern Part of OMZ
http://hdl.handle.net/10174/23966
Title: Thermal Structure in SPZ and Southern Part of OMZ
Authors: Duque, Maria Rosa
Abstract: The last work made by the author with data of heat flow density and thermal conductivity in the South of the country (South Portuguese zone and Southern part of the Ossa Morena Zone ) conjugated with relatively detailed seismic information on the thickness of the crust as well as values of the velocity of seismic waves in the region allowed to define 5 regions with different thermal characteristics.
Using average values of heat flow values obtained from the published data, relative to the region mentioned, it was possible to construct 5 geotherms (temperature curves as a function of depth). The temperature values obtained at the base of the crust (between 616.3 and 647.9 °C) were used to collect information regarding maximum values of density at the top of the lithospheric mantle. Considering that the region is in isostatic equilibrium and using altitude data it is possible to obtain information about the density of the lithosphere and, using the density of the mantle, to obtain crust density values. Although we only have 5 temperature profiles (four profiles in the South Portuguese Zone and one in the Ossa Morena Zone), obtained with average values, it was possible to identify lateral variations of temperature, which undergo changes at different depths. From the comparison of values obtained at two different depths with variations in the velocity of propagation of seismic waves it was possible to establish a relation between temperature values and seismic velocities. Low wave propagation rates will correspond, in principle, to regions with low density value and / or high temperature values.
Recently, studies with seismic data, presenting detailed variations of these parameters, have been published. There are horizontal and vertical profiles of velocity distribution and VP / Vs quotients, which allow us to obtain information about the rheological properties of the crust in the area. The objective of the present work is to obtain detailed information about temperature variation in the region, especially in the upper crust, where the main heat sources responsible for the anomalous values of heat flow measured in these regions (equal or greater than 70 mW/m2) seems to be located. Information will also be obtained for regions not covered by the previous study using radioactivity distribution measured in the region and comparing the values obtained with those of the regions already studied.2018-06-30T23:00:00Z