Observatories and Research Facilities for EUropean Seismology
Volume 6, no 1 July 2004 Orfeus Newsletter

Seismic monitoring for hazard assessment at IST, Lisbon

Joao Fonseca and Carlos Sousa Oliveira

Earthquake Engineering and Seismology Group, ICIST, IST, Lisbon, Portugal

ICIST (Institute for Structure Engineering, Territory and Building Technologies) is a research unit based at IST (Instituto Superior Tecnico), in Lisbon. Through NESS, its Earthquake Engineering and Seismology Group, ICIST is concerned with studies of seismicity, seismic risk and seismotectonics, with emphasis on mainland Portugal and the Azores. In addition, the research goals of NESS include experimental studies of the seismic behaviour of concrete and masonry structures, base isolation systems, etc. Within the scope of a cooperation programme with the authorities of the Republic of Cape Verde, ICIST is also actively involved in volcanic monitoring and volcanic risk mitigation.
Seismological instrumentation by ICIST started in 1996, with the deployment of 12 accelerographs in mainland Portugal (9 instruments) and Azores (3 instruments). This number has increased steadily, and at present ICIST operates a network of 44 strong motion instruments, with the locations shown in Figure 1. Of these, 5 are accessible remotely over a telephone line. Although earthquakes recorded so far had limited magnitude (below M=5.4, except in the Azores), in case of a large earthquake this network will provide key data for the study of local and regional seismic attenuation, and site effects (Oliveira et al., 2002).

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Figure 1

In 1997, ICIST launched the VIGIL project, aimed at instrumenting the volcanic islands of Fogo and Brava in the Cape Verde Archipelago (North Atlantic) for volcanic hazard mitigation (Fonseca et al., 2003). Among the instruments of the VIGIL network are two broadband stations, one in Fogo Island (FPPC) and the other in Brava Island (BCCH), equipped with Guralp CMG-40T sensors and 24-bit DM-24 digitizers. Station data for these and other stations operated by ICIST can be found in the NEIC station book. Continuous 3-component data at 50 sps are transmitted to the central lab in Praia, the Capeverdian capital, over spread-spectrum radio links, were they are stored in a pc using Guralp’s SCREAM!® seismic acquisition software. From the central lab, these data can be retrieved by internet over a dedicated telephone line (shared with the IRIS-IDA station SACV).

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A cooperative effort of ICIST and ORFEUS was initiated in 1999 to make the data from the VIGIL broadband stations available in real-time through the ODC, as part of the VEBSN. It was recognized at an early stage that automatic format conversion from Guralp’s gcf format to a standard format is a key requirement. We were not able yet to solve satisfactorily some technical issues implied by real-time transmission, such as file granularity.

In 2000, ICIST started the deployment of the TAGUSNET network of permanent broadband stations in the Lower Tagus Valley Region around the Portuguese capital, Lisbon. The main purpose of this deployment is to investigate the Lower Tagus Valley fault, towards the refinement of seismic hazard assessment for the Greater Lisbon area (Vilanova and Fonseca, 2004). At present five stations are in operation, two of which transmit in real time to the central lab at ICIST, and three are off-line. The two on-line stations, PMST and PACT, are equipped with CMG-40T sensors and CMG DM-24 digitizers. The data are recorded in a pc with SCREAM!®, for local analysis, and transmitted in real-time to the ORFEUS Data Center by a linux server running a SEEDlink plug-in for format conversion and SeisComP. We are endebted to Reinoud Sleeman from ORFEUS for the adaptation and implementation of the latter software. Additional data requests can be sent to Joao Fonseca.

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Together with the two Cape Verde broadband stations, the on-line stations of the Lower Tagus Valley were integrated in the IP Network, registered at the FDSN.

Project NAVIGATORS (Network of Accelerographs and Very-Broad-Band Instruments for the Gibraltar Azores Transform and Onshore Related Structures) was submitted to the Portuguese Ministry for Science in 1992 by ICIST jointly with colleagues from the Azores and Oporto University, and was recently approved. It aims at the deployment of VBB instruments in the Azores, Madera, NW Africa and Mainland Portugal, and will allow a natural extension of VEBSN towards the Atlantic region over the next few years. Among its goals, this project addresses the possible role of fault interaction in the activation of intraplate faults by the large earthquakes in the plate boundary between Africa and Iberia (Vilanova et al., 2003). To improve coverage in this important seismogenic region, future plans at ICIST contemplate the operation of an OBS BB station off SW Iberia (this goal was already included in the FP6 NERIES proposal).

IST is a member of ORFEUS, IRIS and the FDSN, and the seismologists at ICIST are strongly committed to free real-time dissemination of seismological data to the scientific community.

Acknowledgements

Seismological research at ICIST has been funded by Fundacao para a Ciencia e Tecnologia, Lisbon and ERDF (Projects PPERCAS, VIGIL, TAGUSNET and Plurianual Funding Programme), with additional support from the European Centre for Geodynamics and Seismology. The operation of the strong-motion network has the collaboration of LREC (Azores), and the University of Algarve. Reinoud Sleeman (ORFEUS) is working closely with us towards solving the technical difficulties of distributing the broadband data in SEED format. We are indebted to Pete Davis (UCSD) for letting us share his dedicated line out of Cape Verde.

References

  • Susana P. Vilanova and Joćo F.B.D. Fonseca, in press. The Lower Tagus Valley Fault of SW Iberia. Journal of Seismology, 2004.
  • Susana P. Vilanova, Catarina F. Nunes and Joćo F.B.D. Fonseca, 2003. Lisbon Earthquake of 1755: a case of triggered onshore rupture?Bulletin of the Seismological Society of America, 93(5), pp. 2056-2058.
  • Joćo F.B.D. Fonseca, Bruno V.E. Faria, Nuno P. Lima, Sandra I.N. Heleno, Clara Lįzaro, Nicolas F. d'Oreye, Ana M.G. Ferreira, Inocencio J.M. Barros, Paula Santos, Zuleyka Bandomo, Simon J. Day, Jose P. Osorio, Miguel Baio and Joao L.G. Matos, 2003. Multiparameter Monitoring of Fogo Island, Cape Verde, for Volcanic Risk Mitigation. Journal of Volcanology and Geothermal Research, 125, pp. 35-56.
  • Oliveira, C.S., J. V. Lemos and G.E. Sincraian, 2002. Modelling Large Displacements of Structures Damaged by Earthquake Motions, European Earthquake Engineering, 3, pp 56-71.
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