SEISMOGENIC ZONES AND ATTENUATION LAWS FOR PROBABILISTIC SEISMIC HAZARD Boris LE GOFF ASSESSMENT IN LOW DEFORMATION AREA ZONAS SISMOGÉNICAS E LEIS DE ATENUAÇÃO PARA A ANÁLISE PROBABILÍSTICA DA PERIGOSIDADE SÍSMICA EM REGIÕES DE BAIXA DEFORMAÇÃO Boris LE GOFF Tese apresentada à Universidade de Évora para obtenção do Grau de Doutor em Ciências da Terra e do Espaço Especialidade: Geofísica ORIENTADORES: Mourad BEZZEGHOUD José Fernando BORGES ÉVORA, DEZEMBRO 2013 Contactos: Universidade de Évora Instituto de Investigação e Formação Avançada - IIFA Palácio do Vimioso | Largo Marquês de Marialva, Apart. 94 7002-554 Évora | Portugal Tel: (+351) 266 706 581 INSTITUTO DE INVESTIGAÇÃO E FORMAÇÃO AVANÇADA Fax: (+351) 266 744 677 AND SEISMIC LAWS PROBABILISTIC ASSESSMENT ZONES FOR HAZARD SEISMOGENIC ATTENUATION email: [email protected] ! "# $% &' "() $ Contents Abstract 7 Resumo 9 Résumé 11 List of figures 13 List of tables 15 1. Introduction 17 2. Probabilistic Seismic Hazard Analysis 23 2.1. Introduction.............................................................................................................................25 2.2. Earthquake location: definition of the seismic sources..........................................................26 2.2.1. Conception and geometry of the seismic sources...........................................................26 2.2.1.1. Source zone concept................................................................................................26 2.2.1.2. The different kinds of seismic sources....................................................................27 2.3. Earthquake size and frequency: determination of the magnitude distribution law................28 2.3.1 Magnitude and Epicentral intensity.................................................................................28 2.3.2. Conversions.....................................................................................................................28 2.3.3. Distribution models.........................................................................................................28 2.3.3.1. Determination of complete samples........................................................................28 2.3.3.2. Calculation of the distribution law parameters.......................................................29 2.3.3.2.1. Regression method..........................................................................................29 2.3.3.2.2. Adjustment of the truncated Gutenberg-Richter law.......................................29 2.3.3.2.3 Methodology of maximum likelihood..............................................................30 2.3.3.2.4 Characteristic earthquake model......................................................................30 1 2.3.3.2.5 Gutenberg-Richter law or Characteristic earthquake model?..........................31 2.3.3.3 Maximum Credible Earthquake: determination of the maximum magnitude.........31 2.3.3.3.1. Exploitation of the historical seismicity catalog.............................................31 2.3.3.3.2. Exploitation of the geometric characteristics of the active structures.............32 2.4. Temporal probabilistic models................................................................................................32 2.4.1. Poisson model.................................................................................................................32 2.4.2. Renewal models..............................................................................................................33 2.4.2.1. Definition................................................................................................................33 2.4.2.2. Gamma renewal model...........................................................................................33 2.4.2.3. Weibull renewal model............................................................................................34 2.4.2.4. Log-normal model...................................................................................................34 2.4.2.5 Brownian Passage-Time model................................................................................35 2.5. Ground Motion Prediction Equations (GMPEs).....................................................................36 2.5.1. Classic formulation.........................................................................................................36 2.5.2. Modification of the seismic signal..................................................................................36 2.6. The different kinds of uncertainty...........................................................................................37 2.6.1. Aleatoric uncertainty.......................................................................................................37 2.6.2. Epistemic uncertainty......................................................................................................37 2.6.3. Including uncertainties into PSHA calculations.............................................................37 2.7. Seismic hazard representation................................................................................................38 2.7.1. Hazard curves..................................................................................................................38 2.7.2. Uniform hazard spectrum...............................................................................................39 2.7.3. Hazard maps....................................................................................................................40 2.7.4. De-aggregation of the seismic hazard.............................................................................40 2.8. Conclusion..............................................................................................................................42 3. Seismotectonic context of Portugal 45 3.1 Introduction..............................................................................................................................47 3.2. Geodynamic and Seismotectonic context of the Portugal mainland......................................47 3.3. Seismicity and focal mechanisms...........................................................................................48 3.3.1. Seismicity........................................................................................................................48 3.3.2. Focal mechanisms...........................................................................................................52 3.4 Conclusion...............................................................................................................................55 2 4. Towards a Bayesian seismotectonic zoning 57 4.1. Introduction.............................................................................................................................59 4.2. Input data................................................................................................................................60 4.3. Bayesian methodology reminders...........................................................................................61 4.3.1. Bayesian methods...........................................................................................................61 4.3.2. Graphical models............................................................................................................62 4.3.3. Inference.........................................................................................................................64 4.4. Seismic zoning........................................................................................................................65 4.4.1 Graphical model...............................................................................................................65 4.4.2 Synthetic catalog..............................................................................................................65 4.4.2.1 Temporal repartition of the events...........................................................................66 4.4.2.2 Spatial distribution of the events..............................................................................67 4.4.2.3. Magnitude-frequency relationship..........................................................................68 4.4.3. Bayesian inference..........................................................................................................70 4.4.4. Results.............................................................................................................................73 4.4.5. Uncertainty and variability.............................................................................................77 4.5. Applications............................................................................................................................80 4.5.1. Geoter International example..........................................................................................80 4.5.2. PSHA in Portugal (Villanova and Fonseca, 2007)..........................................................83 4.6. Discussion...............................................................................................................................84 4.7. Conclusion..............................................................................................................................85 5. Historical event relocation and Intensity-distance attenuation law 88 5.1. Introduction.............................................................................................................................90