To estimate where future earthquakes are likely to occur, it is essential to combine information about past earthquakes with knowledge about the location and seismogenic properties of active faults. For this reason, robust probabilistic seismic hazard analysis (PSHA) integrates seismicity and active fault data. Existing seismic hazard assessments for Portugal rely exclusively on seismicity data and do not incorporate data on active faults. Project SHARE (Seismic Hazard Harmonization in Europe) is an EC-funded initiative (FP7) that aims to evaluate European seismic hazards using an integrated, standardized approach. In the context of SHARE, we are developing a fully-parameterized active fault database for Portugal that incorporates existing compilations, updated according to the most recent publications. The seismogenic source model derived for SHARE will be the first model for Portugal to include fault data and follow an internationally standardized approach. This model can be used to improve both seismic hazard and risk analyses and will be combined with the Spanish database for use in Iberian- and European-scale assessments

Besana-Ostman, G.M.

Bezzeghoud, M.

Borges, J.F.

Brum da Silveira, A.

Cabral, J.

Carvalho, J.

Dias, R.P.

Figueiredo, P.M.

Fonseca, J.

Lopes, F.C.

Madeira, J.

Matias, L.

Nemser, E.S.

Perea, H.

Silva, S.

Terrinha, P.

Vilanova, S.

Wong, L.G.

English

Repositório Científico da Universidade de Évora

  SÍS MICA 2010 – 8º CONGRESSO DE SIS MOLOGIA E ENGENHARIA S ÍS MICA 1  COMPILATION OF ACTIVE FAULT DATA IN PORTUGAL FOR USE IN SEISMIC HAZARD ANALYSIS     E.S. NEMS ER1 , J. CABRAL2, P. TERRINHA3, S. VILANOVA1, G.M. BES ANA-OSTMAN1, M. BEZZEGHOUD4, J.F. BORGES4, A. BRUM DA S ILVEIRA2, J. CARVALHO5, R.P. DIAS5, P.M. FIGUEIREDO2, J.F.B.D. FONS ECA6, F.C. LOPES7, J. MADEIRA2, L. MATIAS8, H. PEREA2, S. SILVA3, I.G. WONG9  1- ICIST, Instituto Superior Técnico, Lisboa, Portugal 2- Faculdade de Ciências da Universidade de Lisboa, Departamento de Geologia / Instituto D. Luiz, Lisboa, Portugal 3- Unidade de Geologia Marinha, Laboratório Nacional de Energia e Geologia, Lisboa, Portugal 4- Departamento de Física & Centro de Geofísica de Évora, Escola de Ciências e Tecnologia, Universidade de Évora, Évora, Portugal 5- Laboratório Nacional de Energia e Geologia, Lisboa, Portugal 6- ICIST & Departamento de Física, Instituto Superior Técnico, Lisboa, Portugal 7- Centro de Geofísica, Department of Earth Sciences, University of Coimbra, Coimbra, Portugal 8- Centro de Geofísica da Universidade de Lisboa, Lisboa, Portugal 9- Seismic Hazards Group, URS Corporation, Oakland, California USA   SUMMARY  To estimate where future earthquakes are likely to occur, it is essential to combine informat ion about past earthquakes with knowledge about the location and seismogenic properties of active faults. For this reason, robust probabilistic seismic hazard analysis (PSHA) integrates seismicity and active fault data. Existing seismic hazard assessments for Portugal rely exclusively on seismicity data and do not incorporate data on active faults. Project SHARE (Seis mic Hazard Harmonizat ion in Europe) is an EC-funded initiative (FP7) that aims to evaluate European seismic hazards using an integrated, standardized approach. In the context of SHARE, we are developing a fully-parameterized active fault database for Portugal that incorporates existing compilations, updated according to the most recent publications. The seismogenic source model derived for SHARE will be the first model for Portugal to include fau lt data and follow an internationally standardized approach. This model can be used to improve both seismic hazard and risk analyses and will be combined with the Spanish database for use in Iberian- and European-scale assessments.  1. INTRODUCTION  Active fault databases provide essential input data for robust probabilistic seismic hazard analyses (PSHA) that incorporate both seismicity and active fault data.  Project SHARE is a regional program of the Global Earthquake Model (GEM) init iative, and represents a large collaborative effort to compile a seismic hazard  model fo r the Euro-Mediterranean region to be used for PSHA. The SHARE seismic source model will use a logic tree approach to integrate data on active faults (herein termed “seismogenic sources” following SHARE terminology), seismicity data, and a seismic source zonation model. A major task within SHARE is the compilation of a European database of seismogenic sources; to accomplish this goal, the existing Italian  Database of Individual Seismogenic Sources (DISS) ([1],[2]) is being expanded to include data from the Euro-Mediterranean region. Th is ambitious goal requires the integration of a large amount of data into a unifo rm framework, and requires the adoption of common methodologies and uniform standards for the definition and characterizat ion of active seis mogenic sources.    2 SÍS MICA 2010 – 8º CONGRESSO DE SIS MOLOGIA E ENGENHARIA S ÍS MICA  Project SHARE was designed to follow the SSHAC (Senior Seis mic Hazard Analysis Committee) Level-3 strategy, wherein regional experts present their data to integrators and external experts  in a workshop setting ([3]). The integrators and experts are responsible for evaluating the data and determining how to synthesize the various contributions into a logic tree. SSHAC recommendations describe a strict protocol for incorporating expert opinions and capturing uncertainties in PSHA ([3]);  SSHAC Level-3 guidelines have been recently updated and revised based on lessons learned from a decade of implementing the original guidelines ([4]). A  fundamental aspect of the SSHAC approach is the recognition that true consensus is not a realistic goal, and a more appropriate aim is for a PSHA source model  “to represent the center, body, and range of technical interpretations” of the larger informed technical community ([3]).    2. PRELIMINARY S EIS MOGENIC SOURCE DATABAS E FOR PORTUGAL  Following the SSHAC methodology, a SHARE Iberian regional workshop was held in January 2010 in Olhão, Portugal. This productive meeting brought together researchers from throughout Portugal and Spain to present their research on active fau lting in Iberia. At the Iberian reg ional meet ing, the SHARE Iberian fau lt database was established as a broad, community effort , and researchers were invited to submit their data on seismogenic sources to the regional integrator for incorporation into the SHARE database. The task of compiling seismogenic source data for Portugal to integrate into the Iberian database has been significantly facilitated by the existence of the GIS Seis motectonic Database for Mainland Portugal ([5],[6]). Although this existing seismotectonic database is still in progress, and therefore incomplete, it has provided an excellent starting point for the compilation of seismogenic parameters for the sources in Portugal that wil l be used in the SHARE model.   The GIS Seis motectonic Database for Mainland Portugal contains relevant data for PSHA, though the focus is slightly different because the database was intended to be a repository of active fault data rather than a specific compilation of input data for a PSHA. In the current effort to compile a parameterized seismogenic source database for Portugal, fau lts in Portugal are characterized in terms of “composite seismogenic sources”, following conventions established within the DISS database. Composite seismogenic sources (termed  “seismogenic areas” in [1]; later renamed within the DISS database) are modeled with a complex geometry to capture both geological and geophysical data from large-scale tectonic features and localized geomorphic, geological, or geophysical evidence for active deformat ion ([1]). The composite seismogenic source framework for describing active fau lts was developed specifically fo r use in regional -scale PSHA applications ([1]).   The seismogenic source database for Portugal includes the following fields: source name, compiler name and affiliation, fault location (described as two or more pairs of geographic coordinates), segmentation data, minimum, maximum and preferred values for fault length, fault width, minimum and maximum rupture depth, strike, d ip, rake, slip  rate, and maximum magnitude; preferred values for recurrence interval, single event displacement, style of faulting, most recent earthquake, elapsed time since most recent earthquake, and penultimate earthquake; summaries, notes, links to relevant files, and an indication of the type of evidence that a certain fault exists, according to a specified “quality factor” scheme. For details on the definitions of all seismogenic parameters, see ([2]). The specification of minimum, maximum and preferred values for many of these parameters ensures that the database contains the appropriate epistemic uncertainty ranges to encompass these critical parameters. For consistency with the DISS database, each parameter has an associated code that indicates whether the value is based on 1) literature data, 2) orig inal data, 3) empirical relationships, 4) analytical relationships, or 5) expert judgment ([2]).   The definition of an “active fault” can vary widely, for example, the Quaternary Fault and Fold Database of t he United States includes faults that are considered to have been active during the Quaternary (the past 1,600,000 years) ([7]), whereas the Active Faults Database of New Zealand only includes faults that are known to be active in the Late Quaternary and younger ([8]). For practical purposes in PSHA applications, the appropriate definit ion of an active fault may be different for different tectonic regimes. Due to the slow slip rates in Portugal and the limited body of paleoseismic data, all faults in Portugal with a reasonable likelihood of being active and seismogenic within the current stress regime meet the criteria for inclusion in the SHARE Iberian seismogenic source database.    SÍS MICA 2010 – 8º CONGRESSO DE SIS MOLOGIA E ENGENHARIA S ÍS MICA 3  Whereas a protocol has not yet been established within project SHARE for handling the epistemic uncertainty that pertains to whether or not a specific fault source is active and capable of generating earthquakes, it has been recommended that the seismogenic source database should include a quantification of the likelihood of activ ity of each source. “Probability of Activity” [P(a)] is a system that has been used in  PSHA studies to capture the epistemic uncertainty inherent in the judgment about whether or not a fault is active and seismogenic (e.g., [3]). In the implementation of this system, P(a) occupies the fault database as an independent field and provides a quantification of whether or not a fau lt is active; this uncertainty is then treated in a probabilitistic manner within  the PSHA. Because of the slow slip rates in Portugal and throughout Iberia, there is a substantial amount of uncertainty regarding the Quaternary activity of many faults, and the implementation of a P(a) classificat ion within the database allows for the inclusion of fault sources for which there is some, bu t no definitive data to indicate that they are active. The approach within the existing DISS database to these controversial sources is to label them as “debated seismogenic sources”. However, a shortcoming of that approach is that the debated seismogenic sources are ultimately subject to a binary decision about whether or not they should be included in the source model. In order to accommodate a more robust representation of the potentially active faults in Portugal, the concept of debated seismogenic sources has been replaced with the P(a) scheme within the SHARE database; all faults with a P(a) <1 can be considered as debated sources, and the database can be filtered  according to P(a) for use in the source model, as deemed appropriate.   To develop the database of seismogenic sources in Portugal, all reg ional experts were invited to act as (and be credited as) compilers of the seismogenic parameters. However, in order for the fau lt sources to be included in the SHARE hazard model, it was necessary for the integrators to make informed assumptions to complete the parameter table. These assumptions are preliminary, and will be updated on a case-by-case basis, as appropriate, with the introduction of additional credible data.   To date there are 32 composite seismogenic sources and 74 individual fau lt segments in the preliminary  seismogenic source database for Portugal, which currently  only includes sources on the mainland (Figure 1). The fault with the highest slip rate (≥0.4mm/yr) is the Manteigas -Vilariça-Bragança fault in northeastern Portugal ([9],[10],[11]). Most of the other faults in the database have substantially lower slip rates (preferred slip rate values between 0.01mm/yr and 0.1mm/yr), and are only expected to contribute to the seismic hazard at long return periods. In conjunction with the IBERFAULT meet ing in October 2010, this preliminary database of seismogenic sources in Portugal will undergo a round of revision by regional and external experts in accordance with SSHAC methodology. At this point, the source model will be improved with a greater level of detail, and incorporated into the updated SHARE European fault database.   4 SÍS MICA 2010 – 8º CONGRESSO DE SIS MOLOGIA E ENGENHARIA S ÍS MICA                                            Figure 1. Map of mainland Portugal showing the surface traces of the composite seis mogenic sources in Portugal that are included in the preliminary version of the SHARE Iberia fault database. Segment boundaries are indicated with black dots.    3. ACKNOWLEDGEMENTS  Funding was provided by Project SHARE (FP7-226967) and Project RETURN (FCT-PTDC/CTE-GIN/67367/2006). The SHARE project is financed by the European Commission under the 7th Framework Programme for Research and Technological Development, Area “Environment”, Activity 6.1 “Climate Change, Pollution and Risks”. Th is abstract reflects the author’s views. The European Commission is not liab le for any use that may be made of the informat ion contained therein.      SÍS MICA 2010 – 8º CONGRESSO DE SIS MOLOGIA E ENGENHARIA S ÍS MICA 5  4. REFERENCES   [1] Basili R., Valensise G., Vannoli P., Burrato P., Fracassi U., Mariano S., Tiberti M.M. and Boschi E. (2008) The Database of Individual Seismogenic Sources (DISS), version 3: summarizing 20 years of research on Italy's earthquake geology. Tectonophysics, doi:10.1016/ j.tecto.2007.04.014.  [2] Basili, R., Kastelic, V., Valensise, G. and DISS Working Group 2009 (2009) DISS3 t utorial series: Guidelines for compiling records of the Database of Individual Seis mogenic Sources, version 3. Rapporti Tecnici INGV, 108, 20 p., http://portale.ingv.it/produzione-scientifica/rapporti-tecnici-ingv/archivio/rapporti-tecnici-2009/. [3] SSHAC [Senior Seismic Hazard Analysis Committee, Budnitz, R.J., Chairman, G., Apostolakis, D.M., Boore, L.S., Cluff, K.J., Coppersmith, C.A., Cornell and P.A. Morris] (1997) Recommendations for probabilistic seismic hazard analysis: Guidance on uncertainty and use of experts: Washington, D.C., U.S. Nuclear Regulatory Commission Report, NUREG/CR-6372. [4] Hanks, T.C., Abrahamson, N.A., Boore, D.M., Coppersmith, K.J. and Knepprath, N.E. (2009) Implementation of the SSHAC Guidelines for Level 3 and 4 PSHAs —Experience Gained from Actual Applications. USGS Open-File Report 2009-1093, U.S. Geological Survey, Reston, Virginia, 72 p.  [5] Silva, Í., Cruz, I., Gomes, J., Costa, A., Almeida, P., Cabral, J., Taborda, R., Caranova, R., Laiginhas, C., Angelucci, D., Carrilho, F. and Matias, L. (2008) GIS Seis motectonic database for mainland Portugal. ESIG 2008 - 10º Encontro de Utilizadores de Informação Geográfica, 14 - 16 de Maio, Taguspark, Oeiras, Portugal. 10p. [6] Cabral, J. (1995) Neotectónica em Portugal Continental, Memórias do Instituto Geológico e Mineiro, Memória 31, Lisbon, 265 p. [7] U.S. Geological Survey (2006) Quaternary fault and fold database for the United States, accessed 06/23/2010, from USGS web site: http//earthquakes.usgs.gov/regional/qfaults/. [8] GNS http://data.gns.cri.nz/af/. [9] Rockwell, T., Fonseca, J., Madden, C., Dawson, T., Owen, L.A., Vilanova, S. and Figueiredo, P. (2009) Paleoseismology of the Vilariça segment of the Manteigas -Bragança Fault in northeastern Portugal. In: Palaeoseismology: Historical and Prehistorical Records of Earthquake Ground Effects for Seismic Hazard  Assessment (Reicherter, K., Michetti, A.M. & Silva, P. G., eds.). The Geological Society, London, Special Publications, 316, 237-258. [10] Cabral, J. (1989) An example of interplate Neotectonic activity, Vilariça Basin, Northeast Portugal. Tectonics, 8 (2), 285-303. [11] Vilanova, S. and Fonseca, J. F. B. D. (2007) Probabilistic seismic-hazard assessment for Portugal. Bulletin  of the Seis mological Society of America, 97, 1702-1717. 

COMPILATION OF ACTIVE FAULT DATA IN PORTUGAL FOR USE IN SEISMIC HAZARD ANALYSIS

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COMPILATION OF ACTIVE FAULT DATA IN PORTUGAL FOR USE IN SEISMIC HAZARD ANALYSIS

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