Abstract
The Portuguese mainland territory is located in a tectonic setting responsible for significant neotectonic and seismic activities. The regional geodynamical evolution is dominated by the slow convergence (c. 2mm/year) of Eurasia and Africa in a NNW-SSE to NW-SE direction along the eastern segment of the Azores-Gibraltar plate boundary (AGPB). This tectonic framework explains the history of destructive earthquakes and tsunamis recorded along the Portuguese coast. Of these, the most significant event known was the Lisbon earthquake of 1 November 1755 with an assumed origin at the Goringe Bank and attaining an extreme magnitude (83/4). The tsunami generated by this event produced large destruction along the Iberian and Morocco coasts. The need to reduce the social and economic impact of the large historical events reported, led to the intensive research on the seismicity affecting Portugal Mainland, namely, long and medium term prediction, characterization of microseismicity through the improvement of the available seismic network and development of a Tsunami Warning System.
The long term prediction was produced assuming a Gutenberg-Richter law for the time occurrence of earthquakes but for medium term prediction of large earthquakes (M>5.8) for the western Iberia area it was used the Keilis-Borok methodology. The Time of Increased Probability (TIP) windows seems to be a useful technique for assessing the seismic hazard, as has been shown in the Pacific Area. For even shorter term predictions a multi-disciplinary and continuous geophysical survey of the source areas must be developed. One of the long established phenomena associated with the occurrence of strong earthquakes is the alteration of source seismicity and microseismicity. In order to address the question of “how well is our seismic network designed to characterize the small scale seismicity and their changes” the seismic network design was studied under the assumptions of Information Theory. In particular, the best location for an additional station is defined by the one that maximizes the net information transfer.
The installation of an Ocean Bottom Observatory including a broadband seismic station is of the utmost importance for the monitoring of the most important seismogenic and tsunamigenic area, the Goringe bank. As the travel-time for tsunamis generated in this area exceed 30 minutes for nearby coast line we were able to design and develop a pilot destructive earthquake and tsunami warning system (DETWS) that could give almost realtime warnings for the civil authorities.
The extensive experience in monitoring natural seismic sources can be very useful when designing a control system for strong artificial sources such as nuclear explosions. The lessons to be learned can be summarized as follows: study as thorough as possible all past experiences, design the best monitoring network using objective criteria and evaluate its performance, install when possible near source sensors and/or complementary systems in remote areas such as the ocean bottom.
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References
Cabral, J. (1993) Neotectónica de Portugal Continental, Ph.D. thesis, Fac. Ciências Univ. Lisboa.
Sartori, R., Torelli, L., Zitellini, N., Peis, D. and Lodolo, E. (1994) Eastern segment of the Azores-Gibraltar line (central-eastern Atlantic): An oceanic plate boundary with diffuse compressional deformation, Geology 22, 555–558.
Martins, I. and Mendes-Victor, L. A. (1990) Contribuição Para o Estudo da Sismicidade de Portugal Continental, Univ. de Lisboa, Inst. Geof. Infante D. Luis, Pub. nº18.
Martins, I. and Mendes-Victor, L. A. (1993) Actividade Sísmica na Região Oeste da Península Ibérica, Energética e Períodos de Retorno, Univ. de Lisboa, Inst. Geof. Infante D. Luis, Pub. nº20.
Heinrich, Ph., Baptista, M.A. and Miranda, P. (1994) Numerical simulation of 1969 tsunami along the Portuguese coasts. Preliminary results, Science of Tsunami Hazards 10, nº1, 3–23.
Fukao, Y. (1973) Thrust faulting at a lithospheric plate boundary, the Portugal earthquake of 1969, Earth and Planet. Sc. Letters 18, 205–216.
Simões, J.Z., Afilhado, A. and Mendes-Victor, L.A. (1992) Assessing the tsunami risk using instrumental and historical records, Science of Tsunami Hazards 10, nº1, 3–7.
Martins, I. and Mendes-Victor, L. A. (1994) Contribuição para o Estudo da Predição Sísmica a Médio Prazo (Aplicação à Região Oeste da Peninsula Ibérica), Univ. de Lisboa, Inst. Geof. Infante D. Luis, Pub. nº23.
Gabrielov, A.M., et al. (1986) Algorithm of Long-Term Earthquake Prediction, Ceresis -Centro Regional de Sismologia para a America do Sul.
Keilis-Borok, V.I. and Rotvain, I.M. (1988) Diagnosis of Time of Increased Probability of Strong Earthquakes in Different Regions of the World: Algorithm CN, Institute of Physics of the Earth, Academy of Sciences of the U.S.S.R., Moscow.
Keilis-Borok, V.I. and Soloviev, A.A. (1988) Pattern Recognition in Earthquake Prediction, Institute of Physics of the Earth, Academy of Sciences of the U.S.S.R., Moscow.
Senos, M.L., Reis, P.A. and Vales, D. (1994) Modernização da rede sismográfica nacional, in 2º Encontro Sobre Sismologia e Engenharia Sísmica, Fac. Eng. Univ. Porto, I.45-I.53.
Matias, L.M. and Peixoto, J.P. (1994) Entropia e Sismologia, Univ. de Lisboa, Inst. Geof. Infante D. Luis, Pub. nº21.
Mendes Victor, L. A., Baptista, M. A. and Simões, J. Z. (1991) Destructive Earthquakes and Tsunami Warning System, Terra Nova 32, 119–121.
Simões, J. Z., Monteiro, A. and Mendes Victor, L. (1992) On-line Data Processing with Microcomputers for Low-Power Satellite Transmission, Cahiers du CEGS 5, 111–120.
Simões, J. Z., Afilhado, A. and Mendes Victor, L. A. (1993) Complementary Land-Based Tsunami Warning System in SW Portugal, in S.Tinti (ed.), Tsunamis in the World, 217–228.
Okal, E.A. and Talandier, J. (1991) Single station estimates of the seismic moment of the 1960 Chilean and 1964 Alaskan earthquakes, using the mantle magnitude Mm, Pure Applied Geophys. 136, 103–126.
Reymond, D., Hyvermaud, O. and Talandier, J. (1991) Automatic detection location and quantification of earthquakes: Application to tsunami warning, Pure applied Geophys. 125, nº3 361–382.
Berg, E. and Chesley, D.M. (1976) Automated high-precision amplitude and phase calibration of seismic systems, Bull. Seism. Soc. Am. 66, 1413–1424.
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Mendes-Victor, L.A., Peixoto, J.P., Matias, L.M., Martins, I., Simões, J.Z., Baptista, M.A. (1996). Monitoring Earthquake Activity Offshore Iberia. In: Husebye, E.S., Dainty, A.M. (eds) Monitoring a Comprehensive Test Ban Treaty. NATO ASI Series, vol 303. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-0419-7_26
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DOI: https://doi.org/10.1007/978-94-011-0419-7_26
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