Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site
Tóm tắt
The Lower Tagus Valley has experienced significant (M 6–7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.
Tài liệu tham khảo
Bishop AW (1955) The use of the slip circle in the stability analysis of slopes. Geotechnique 1:7–17
Borges JF, Fitas AJS, Bezzeghoud M, Teves-Costa P (2001) Seismotectonics of Portugal and its adjacent Atlantic area. Tectonophysics 337:373–387
Cabral J (1995) Neotectónica em Portugal Continental. Memórias do Instituto Geológico e Mineiro, 31, Lisboa
Cabral J, Marques FMSF (2001) Paleoseismological studies in Portugal: Holocene thrusting or landslide activity? EOS Transactions 82:351–352
Cabral J, Marques F, Figueiredo P (2002) Paleoseismicity evidence in the Lower Tagus Valley (Lisbon Region)? An example of misinterpretation of geological data. 3a Assembleia Luso-Espanhola de Geodesia e Geofísica, Univ. Polit. de Valencia, 4–8 Fev. 2002, Proceedings I, pp 386–389
Cabral J, Marques F, Figueiredo P, Simão N, Matias L (2003) New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley). Ciências da Terra N.Esp. 5, VI Congresso Nacional de Geologia, Junho 2003, UNL, Caparica, D10–D13 (CD-ROM)
Cabral J, Ribeiro P, Figueiredo P, Pimentel N, Martins A (2004) The Azambuja fault: an active structure located in an intraplate basin with significant seismicity (Lower Tagus Valley, Portugal). J Seismol 8:347–362
Carrilho F, Nunes JC, Pena J, Senos ML (2004) Catálogo Sísmico de Portugal Continental e Região Adjacente para o período 1970–2000, Instituto de Meteorologia, Lisboa, ISBN 972-9083-12-6
Carvalho J (2003) Sísmica de alta resolução aplicada à prospecção, geotecnia e risco sísmico. PhD Dissertation, Universidade de Lisboa
Carvalho J, Cabral J, Gonçalves R, Torres L, Mendes-Victor L (2006) Geophysical methods applied to fault characterization and earthquake potential assessment in the Lower Tagus Valley, Portugal. Tectonophysics 418:277–297
Carvalho J, Rabeh T, Cabral J, Carrilho F, Miranda JM (2008) Geophysical characterization of the Ota–Vila Franca de Xira–Lisbon–Sesimbra fault zone, Portugal. Geophys J Int 174:567–584
Coelho AG (2001) Historia de las laderas de Santarém (Portugal). Problemas de estabilización de laderas alcantiladas coronadas por un estrato rocoso. V Simposio Nacional sobre Taludes y Laderas Inestables, vol I, CEDEX, Madrid
Fonseca FBD, Meghraoui M, Bosi V, Cardoso JL, Oosterbeek L (2000a) ECGS Field Trip to the Lower Tagus Valley, Portugal, Lisbon, 9th of September 2000, Guide Book, ECGS, FCT, IST, Lisbon
Fonseca FBD, Bosi V, Vilanova SP, Meghraoui M (2000b) Investigations unveil Holocene thrusting for onshore Portugal. EOS Transactions 81:412–413
Fonseca FBD, Bosi V, Vilanova SP, Meghraoui M (2001) Paleoseismological studies near Lisbon: Holocene thrusting or landslide activity?—reply. EOS Transactions 82:352–353
Gràcia E, Dañobeitia J, Vergés J, the PARSIFAL Team (N Zitellini, M Rovere, D Accetella, A Ribeiro, J Cabral, L Matias, R Bartolomé, M Farrán, D Casas, A Maldonado, A Pazos, D Córdoba, X Roset) (2003) Mapping active faults offshore Portugal (36°N–38°N): implications for seismic hazard assessment along the southwest Iberian margin. Geology 31:83–86
Henriques MC, Mouzinho MT, Ferrão NM (1988) Sismicidade de Portugal. O Sismo de 26 de Janeiro de 1531. Comissão para o Catálogo Sísmico Nacional, Lisbon
IGeoE - Instituto Geográfico do Exército (2005) Carta Militar de Portugal Série M888, Folha 364-Cartaxo, ISBN:972-765-264-6
Jambu N (1954) Application of composite slip surface for stability analysis. European Conference on Stability of Earth Slopes, Stockholm, Sweden
Justo JL, Salwa C (1998) The 1531 Lisbon earthquake. Bull Seismol Soc Am 88:319–328
Martins AA (1999) Caracterização morfotectónica e morfosedimentar da Bacia do Baixo Tejo (Pliocénico e Quaternário). PhD Dissertation, Universidade de Évora
Martins AA, Barbosa B (1992) Planaltos do Nordeste da Bacia Terciária do Tejo (Portugal). Comun Serv Geol Port 78(1):13–22
Martins I, Mendes-Víctor LA (2001) Contribuição para o estudo da sismicidade de Portugal Continental. Instituto Geofísico do Infante D. Luís, Publ. 25, Universidade de Lisboa
Martins AA, Cunha PP, Huot S, Murray AS, Buylaert JP (2009) Geomorphological correlation of the tectonically displaced Tejo River terraces (Gavião–Chamusca area, central Portugal) supported by luminescence dating. Quat Int 199:75–91
McCalpin JP, Carver GA (2009) Paleoseismology of compressional tectonic environments. In: McCalpin JP (ed) Paleoseismology. 2nd edn. Academic, Burlington, pp 315–419
Mendonça JL, Cabral J (2003) Identificação de falhas na Bacia Cenozóica do Tejo através de técnicas de investigação hidrogeológica. Comun Inst Geol Min 90:91–102
Mezcua J (1982) Catalogo General de Isossistas de la Peninsula Iberica. Publicación 202, Instituto Geografico Nacional, Madrid
Moreira VS (1984) Sismicidade histórica de Portugal Continental. Rev Inst Nac Meteorol Geofís 3:3–79
Moreira VS (1985) Seismotectonics of Portugal and its adjacent area in the Atlantic. Tectonophysics 117:85–96
Moreira VS (1991) Historical seismicity and seismotectonics of the area situated between the Iberian Peninsula, Morocco, Selvagens and Azores Islands. In: Mezcua J, Udías A (eds) Seismicity, seismotectonics and seismic risk of the Ibero-Maghrebian Region, publicacion I.G.N. Série monografia n. 8. Instituto Geografico Nacional, Madrid, pp 213–225
Morgenstern NR, Price VE (1965) The analysis of the stability of general slip surfaces. Geotechnique 15:79–93
Oliveira R (1973) An example of the influence of lithology on slope stability. Geotecnia 6:7–17
Oliveira CS (1986) A Sismicidade Histórica e a Revisão do Catálogo Sísmico. Proc. 36/11/7368, I e D, Estruturas, Relatório 99/86—NDA, LNEC, Lisboa
Oliveira JT, Pereira E, Ramalho M, Antunes MT, Monteiro JH (coord.) (1992) Carta Geológica de Portugal, Escala 1:500.000, Instituto Geológico e Mineiro, Lisboa
Peláez JAM, Casado CL, Romero JH (2002) Deaggregation in magnitude, distance, and azimuth in the South and West of the Iberia Peninsula. Bull Seismol Soc Am 92:2177–2185
Ramos C, Reis E, Pereira AR, Azevêdo TM, Nunes E, Freitas, MC, Andrade C (2002) Late Holocene evolution of the Lower Tagus alluvial plain and heavy metals content: preliminary results. In: Garcia-Ruiz JM, Jones JAA, Armáez J (eds) Environmental change and water sustainability, study group on water sustainability of the int. geog. unit, Zaragoza, pp 167–182
Rasmussen ES, Lomholt S, Andersen C, Vejbæk OV (1998) Aspects of the structural evolution of the Lusitanian Basin in Portugal and the shelf and slope area offshore Portugal. Tectonophysics 300:199–225
Ribeiro A, Kullberg MC, Kullberg JC, Manupella G, Phipps S (1990) A review of Alpine tectonics in Portugal: foreland detachment in basement and cover rocks. Tectonophysics 184:357–366
Ribeiro A, Cabral J, Batista R, Matias LM (1996) Tectonic stress pattern in Portugal mainland and the adjacent Atlantic region (West Iberia). Tectonics 15:641–659
Simão NMM (2003) Aplicações de Sísmica de Reflexão e Refracção na Geotecnia. Graduation Dissertation, Universidade de Lisboa
Sousa ML, Martins A, Oliveira CS (1992) Compilação de catálogos sísmicos da região ibérica. Proc. 36/11/9295, Laboratório Nacional de Engenharia Civil, Lisboa
Stich D, Batlló J, Macià R, Teves-Costa P, Morales J (2005) Moment tensor inversion with single-component historical seismograms: the 1909 Benavente (Portugal) and Lambesc (France) earthquakes. Geophys J Int 162:850–858
Terrinha P, Pinheiro LM, Henriet J-P, Matias L, Ivanov MK, Monteiro JH, Akhmetzhanov A, Volkonskaya A, Cunha T, Shaskin P, Rovere M, the Ttr10 Shipboard Scientific Party (2003) Tsunamigenic-seismogenic structures. Neotectonics, sedimentary processes and slope instability on the southwest Portuguese margin. Mar Geol 195:55–73
Teves-Costa P, Rio I, Marreiros C, Ribeiro R, Borges JF (1999) Source parameters of old earthquakes: semi-automatic digitization of analog records and seismic moment assessment. Nat Hazards 19:205–220
Vilanova SP (2003) Sismicidade e perigosidade sísmica do Vale Inferior do Tejo, Ph.D. Dissertation, Instituto Superior Técnico, Lisboa
Vilanova SP, Fonseca JFBD (2004) Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia). J Seismol 8:331–345
Vilanova SP, Nunes CF, Fonseca JFBD (2003) Lisbon 1755: a case of triggered onshore rupture? Bull Seismol Soc Am 93:2056–2068
Vis G-J (2009) Fluvial and marine sedimentation at a passive continental margin. The late Quaternary Tagus depositional system. PhD. Dissertation, VU University Amsterdam
Vis G-J, Kasse C, Vanderberghe J (2008) Late Pleistocene and Holocene palaeogeography of the Lower Tagus Valley (Portugal): effects of relative sea level, valley morphology and sediment supply. Quat Sci Rev 27:1682–1709. doi:10.1016/j.quascirev.2008.07.003
Zitellini N, Chierici F, Sartori R, Torelli L (1999) The tectonic source of the 1755 Lisbon earthquake and tsunami. Ann Geophys 42:49–55
Zitellini N, Mendes Victor LA, Cordoba D et al (2001) The 1755 Lisbon earthquake and tsunami: localization and investigation of the tectonic source. EOS, Transactions, Am Geophys Union 82:290–291
Zitellini N, Rovere M, Terrinha P, Chierici F, Matias L, BIGSETS Team (2004) Neogene through quaternary tectonic reactivation of SW Iberian Passive Margin. Pure Appl Geophys 161:567–587