Antonio Emolo with Vincenzo Convertito and Aldo Zollo

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

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

3. PSHA basic steps (Cornell, 1968) • Seismogenetic zone • Seismicity recurrence characteristics • Earthquakes effects • Hazard evaluation Antonio Emolo

4. 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 Antonio Emolo

5. For doing this we need • the magnitude distribution • the seismicity rate for a single fault/magnitude earthquake • a (deterministic) tool for evaluating earthquake effects • a statistical description of (deterministic) earthquake effects Antonio Emolo

6. The Colfiorito earthquake: source parameters After Zollo et al., 1999 Antonio Emolo

7. The Colfiorito earthquake: simulation facts • number of simulated rupture processes: 150 • investigated area: 60×60 km2 • number of receivers: 64 • spacing between adjacent receivers: 5 km Antonio Emolo

8. The Colfiorito earthquake: simulation results Antonio Emolo

9. 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 Antonio Emolo

10. average seismicity rates: c=0.00204 yrs-1 exp=0.155 yrs-1 from simulation study we do not need! both characteristic and exponential models b-value = 0.8475 Coming back to the hazard integral Antonio Emolo

11. Hazard maps in terms of PGA values having a fixed frequency of exceedance corresponding to three return periods: T1=1,000 yrs T2=5,000 yrs T3=10,000 yrs Antonio Emolo

12. Hazard maps – T=1,000 yrs Antonio Emolo

13. Hazard maps – T=5,000 yrs Antonio Emolo

14. Hazard maps – T=10,000 yrs Antonio Emolo

15. Hazard curves for selected sites characteristic earthquake model Antonio Emolo

16. Hazard curves for selected sites exponential magnitude distribution Antonio Emolo

17. I nearly forgot: are PGAs log-normally distributed? Antonio Emolo

18. In conclusion • 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; • 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 Antonio Emolo

19. 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 Antonio Emolo

20. And finally, that’s all Thank you very much for your kindly attention Antonio Emolo

21. ZS9 – Meletti and Valensise, 2004 Seismogenetic zone • Each zone has uniform earthquake potential • The configuration could be point line area volume Antonio Emolo

22. Seismicity recurrence characteristics Recurrence relationship (e.g., Gutenberg and Richter, 1944) Antonio Emolo

23. 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; …) Antonio Emolo

24. For a given time of interest t, the probability of exceedance can be computed as frequency of exceedance of a given threshold A0 seismic activity rate (from catalogues) 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) probability of exceedance of a threshold value A0 for given distance r and magnitude m 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 Antonio Emolo

25. Hazard evaluation Antonio Emolo

26. Hazard evaluation Antonio Emolo

27. 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 Antonio Emolo

28. The magnitude distribution Antonio Emolo

29. 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) Antonio Emolo

30. 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) Antonio Emolo

31. 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 Antonio Emolo

32. Statistical description of earthquake effects Antonio Emolo