Prague, March 18, 2005Antonio Emolo1 Seismic Hazard Assessment for a Characteristic Earthquake Scenario: Integrating Probabilistic and Deterministic Approaches Antonio Emolo with Vincenzo Convertito and Aldo Zollo Prague, March 18, 2005

Antonio Emolo2 Table of Contents Brief review of Probabilistic Seismic Hazard Analysis technique Brief review of Probabilistic Seismic Hazard Analysis technique Integration of Probabilistic and Deterministic approaches to seismic hazard Integration of Probabilistic and Deterministic approaches to seismic hazard Application to the September 26, 1997, 9:40GMT, Colfiorito (Central Italy) earthquake, M W =6.0 Application to the September 26, 1997, 9:40GMT, Colfiorito (Central Italy) earthquake, M W =6.0

Prague, March 18, 2005Antonio Emolo3 PSHA basic steps (Cornell, 1968) Seismogenetic zone Seismogenetic zone Seismogenetic zone Seismogenetic zone Seismicity recurrence characteristics Seismicity recurrence characteristics Seismicity recurrence characteristics Seismicity recurrence characteristics Earthquakes effects Earthquakes effects Earthquakes effects Earthquakes effects Hazard evaluation Hazard evaluation Hazard evaluation Hazard evaluation

Prague, March 18, 2005Antonio Emolo4 In our proposed approach we aim at applying the classical PSHA technique to the single fault case by integrating PSHA with a statistical - deterministic technique for predicting strong ground motion parameters associated with a characteristic earthquake occurring on a given causative fault

Prague, March 18, 2005Antonio Emolo5 For doing this we need the magnitude distribution the magnitude distribution the magnitude distribution the magnitude distribution the seismicity rate for a single fault/magnitude earthquake the seismicity rate for a single fault/magnitude earthquake the seismicity rate for a single fault/magnitude earthquake the seismicity rate for a single fault/magnitude earthquake a (deterministic) tool for evaluating earthquake effects a (deterministic) tool for evaluating earthquake effects a (deterministic) tool for evaluating earthquake effects a (deterministic) tool for evaluating earthquake effects a statistical description of (deterministic) earthquake effects a statistical description of (deterministic) earthquake effects a statistical description of (deterministic) earthquake effects a statistical description of (deterministic) earthquake effects

Prague, March 18, 2005Antonio Emolo6 The Colfiorito earthquake: source parameters fault length, L 12 km fault width, W 7.5 km bottom depth, z max 8.0 km strike, Φ 152° dip, δ 38° slip, λ -118° seismic moment, M 0 1.0×10 18 Nm moment magnitude, M W 6.0 rupture velocity, v R 2.7 km/s After Zollo et al., 1999

Prague, March 18, 2005Antonio Emolo7 The Colfiorito earthquake: simulation facts number of simulated rupture processes: 150 number of simulated rupture processes: 150 investigated area: 60×60 km 2 investigated area: 60×60 km 2 number of receivers: 64 number of receivers: 64 spacing between adjacent receivers: 5 km spacing between adjacent receivers: 5 km

Prague, March 18, 2005Antonio Emolo8 The Colfiorito earthquake: simulation results

Prague, March 18, 2005Antonio Emolo9 The Colfiorito earthquake: simulation results Simulated PGAs vs. minimum distance from the surface fault projection are compared with the Sabetta and Pugliese (1987) attenuation curve for a magnitude 6.0 earthquake

Prague, March 18, 2005Antonio Emolo10 from simulation study both characteristic and exponential models b-value = we do not need! average seismicity rates:  c = yrs -1  exp =0.155 yrs -1 Coming back to the hazard integral

Prague, March 18, 2005Antonio Emolo11 Hazard maps in terms of PGA values having a fixed frequency of exceedance corresponding to three return periods: T 1 =1,000 yrs T 2 =5,000 yrs T 3 =10,000 yrs

Prague, March 18, 2005Antonio Emolo12 Hazard maps – T=1,000 yrs

Prague, March 18, 2005Antonio Emolo13 Hazard maps – T=5,000 yrs

Prague, March 18, 2005Antonio Emolo14 Hazard maps – T=10,000 yrs

Prague, March 18, 2005Antonio Emolo15 Hazard curves for selected sites characteristic earthquake model

Prague, March 18, 2005Antonio Emolo16 Hazard curves for selected sites exponential magnitude distribution

Prague, March 18, 2005Antonio Emolo17 I nearly forgot: are PGAs log-normally distributed?

Prague, March 18, 2005Antonio Emolo18 In conclusion we account for time variable (return period, time of interest, …) in deterministic scenarios; we account for time variable (return period, time of interest, …) in deterministic scenarios; we account for source parameters (geometry, radiation pattern, directivity, …) in PSHA approach; we account for source parameters (geometry, radiation pattern, directivity, …) in PSHA approach; due to the waveforms availability, we can consider any ground motion parameter both in time and in frequency domains due to the waveforms availability, we can consider any ground motion parameter both in time and in frequency domains we can easily include site effects in the modeling if specific transfer function was available we can easily include site effects in the modeling if specific transfer function was available

Prague, March 18, 2005Antonio Emolo19 Before ending… I would like to thank the MAGMA center and all the people who gave me the opportunity to spend a very useful period at the Charles University

Prague, March 18, 2005Antonio Emolo20 And finally, that’s all Thank you very much for your kindly attention

Prague, March 18, 2005Antonio Emolo21 Seismogenetic zone ZS9 – Meletti and Valensise, 2004 Each zone has uniform earthquake potential Each zone has uniform earthquake potential The configuration could be The configuration could bepointlineareavolume

Prague, March 18, 2005Antonio Emolo22 Seismicity recurrence characteristics Recurrence relationship (e.g., Gutenberg and Richter, 1944)

Prague, March 18, 2005Antonio Emolo23 Earthquakes effects The ground motion level at a given site and for a selected range of magnitude is generally evaluated through empirical attenuation relationships (e.g., Joyner and Boore, 1981; Sabetta and Pugliese, 1986; …)

Prague, March 18, 2005Antonio Emolo24 probability of exceedance of a threshold value A 0 for given distance r and magnitude m probability of occurrence of a given earthquake having magnitude in the range (m, m+dm) probability of occurrence of a given earthquake at a distance in the range (r, r+dr) seismic activity rate (from catalogues) Hazard evaluation It consists in the computation of the probability of exceedance of different levels of selected ground motion parameter A thorough the evaluation of the hazard integral frequency of exceedance of a given threshold A 0 For a given time of interest t, the probability of exceedance can be computed as

Prague, March 18, 2005Antonio Emolo25 Hazard evaluation

Prague, March 18, 2005Antonio Emolo26 Hazard evaluation

Prague, March 18, 2005Antonio Emolo27 The characteristic earthquake model is based on the hypothesis that individual fault tend to generate similar size (i.e., “characteristic”) earthquakes Characteristic earthquakes occur on a fault not at the exclusion of all other magnitude events, but with a frequency distribution which differs from the exponential one Several paleoseismic evidences in different tectonic environments support the idea that geometry, mechanism and average slip per event could be considered constant over a large time scale

Prague, March 18, 2005Antonio Emolo28 The magnitude distribution

Prague, March 18, 2005Antonio Emolo29 The seismicity rate It can be evaluated both for the exponential model and for the characteristic earthquake model following the approach proposed by Youngs and Coppersmith (1985)

Prague, March 18, 2005Antonio Emolo30 Earthquake effects Seismic radiation emitted by an extended rupturing fault is computed by solving the representation integral in high frequency approximation (Aki and Richards, 1980) The HF Green function is computed in a flat-layered velocity medium The slip function is approximated by a ramp A k-squared final slip distribution on the fault is assumed (Herrero and Bernard, 1996)

Prague, March 18, 2005Antonio Emolo31 Statistical description of earthquake effects In the frame of a scenario simulation associated with a characteristic earthquake, some “low frequency” source characteristics can be considered constant over a large time scale in successive rupture episodes. However the single rupture process does not repeat the same style of nucleation, propagation and stopping even if it keeps the mean characteristics. With this in mind, we simulated a large number of rupture processes occurring on the same causative fault considering different positions of nucleation point and different final slip distributions. Synthetic seismograms are computed for each considered rupture process and ground motion parameters of interest are then evaluated through a statistical analysis

Prague, March 18, 2005Antonio Emolo32 Statistical description of earthquake effects