3D Numerical Simulations of Earthquake Ground Motion in Sedimentary Basins: Gubbio and L'Aquila Cases

1. 3D NUMERICAL SIMULATIONS OF EARTHQUAKE GROUND MOTION IN SEDIMENTARY BASINS: THE CASES OF GUBBIO AND L’AQUILA, CENTRAL ITALY Roberto Paolucci and Chiara Smerzini Department of Structural Engineering, Politecnico di Milano

2. Contents • Motivation for 3D numerical simulations of earthquake ground motion • The spectral element code GeoELSE • Case studies • Seismic response of the Gubbio basin during the 1997 Umbria-Marche earthquake • Modeling of the MW 6.3 2009 L’Aquila earthquake • Conclusions

3. 3 3D earthquakegroundmotionnumericalsimulations Objective To simulate “synthetic earthquakes” as realistic as possible in terms of: • the complexity of the seismic source • the complexity of the geological and morphological environment • the frequency range of the seismic excitation

4. 3D earthquakegroundmotionnumericalsimulations Applications parametric studies on earthquake ground motion PGV maps in the Grenoble Valley due to a Mw6 earthquake along the Belledonne fault. From left to right: neutral, forward, backward directivity conditions with respect to the urban area of Grenoble. After Stupazzini et al., 2009.

5. seismic input for strategic structures PGV (cm/s) 3D earthquakegroundmotionnumericalsimulations Applications seismic risk assessment of urban areas under scenario earthquakes integration to PSHA, especially for long return periods ShakeOut Scenario: Southern California (Tech. report, 2008) - CyberShake (Graves et al., 2010) - S2 Project DPC-INGV 2007-2009 (Faccioli et al, 2010) after the Japanese guidelines for evaluation of seismic hazard for nuclear installations (IAEA, 2010)

6. 3D earthquakegroundmotionnumericalsimulations

7. Contents • Motivation for 3D numerical simulations of earthquake ground motion • The spectral element code GeoELSE • Case studies • Seismic response of the Gubbio basin during the 1997 Umbria-Marche earthquake • Modeling of the MW 6.3 2009 L’Aquila earthquake • Conclusions

8. The SpectralElement code GeoELSE Web site: http://geoelse.stru.polimi.it • Developers • Department of Structural Engineering, Politecnico di Milano • E. Faccioli, R. Paolucci, L. Scandella, C. Smerzini, M.Stupazzini, M. Vanini • CRS4 (Center of Advanced Studies, Research and Development in Sardinia) • F. Maggio, L. Massidda • Department of Modeling and Scientific Computing (MOX), Politecnico di Milano • P. Antonietti,I. Mazzieri, A. Quarteroni, F. Rapetti

9. The Spectral Element code GeoELSE Main purpose of GeoELSE Studying 2D/3D linear and non-linear visco-elastic seismic wave propagation in heterogeneous media, including within the same numerical model: - seismic source (extended fault / plane wave with arbitrary incidence angle) - propagation path -complex geological structures / SSI effects

10. L’Aquila basin • 10 The SpectralElement code GeoELSE Traffic-induced vibrations Dynamic Soil Structure Interaction Seismic wave propagation in complex geological configurations Dynamic response of structures

11. The SpectralElement code GeoELSE Some “historical” references on spectral approaches for the numerical integration of the wave equation Kosloff D, Baysal E. Forward modelling by the Fourier method Geophysics 1982 47: 1402-1412. • Kosloff D, Kessler D, Filho AQ, Tessmer E, Behle A, Strahilevitz R. • Solutions of the equations of dynamics elasticity by a Chebyshev spectral method • Geophysics 1990; 55: 748-754. • Faccioli E, Maggio F, Paolucci R, Quarteroni A. • 2D and 3D elastic wave propagation by a pseudo-spectral domain decomposition method • Journal of Seismology 1997; 1 237-251. • Komatitsch D, Vilotte J-P. • The spectral element method: an efficient tool to simulate the seismic response of 2D and 3D geological structures. • Bull. Seism. Soc. Am. 1998; 88: 368-392.

12. N = 4 The Spectral Element code GeoELSE • Spatial discretization unstructured hexahedral SEs • Numerical integration Legendre-Gauss-Lobatto (LGL) rule • Polynomial basis (test functions) orthogonal Lagrangepolynomials of degree N (Spectral Degree) • Time discretization: explicit 2nd order FD(LF2-B2) • Native implementation in parallel architectures MPI (Message Passing Interface)

13. 13 Treatment of seismic input in GeoELSE • plane wave incidence with arbitrary angles (engineering applications) • kinematic modeling of a seismic fault with spatially varying source parameters (seismic hazard evaluations, seismic scenarios)

14. Contents • Motivation for 3D numerical simulations of earthquake ground motion • The spectral element code GeoELSE • Case studies • Seismic response of the Gubbio basin during the 1997 Umbria-Marche earthquake • Modeling of the MW 6.3 2009 L’Aquila earthquake • Conclusions

15. Case studies Sedimentary basins in Central Italy related to extensional tectonic activity Gubbio Norcia Rieti L’Aquila Avezzano Sulmona

16. 3D seismicresponse of the Gubbio basin The 1997-1998 Umbria Marche seismic sequence GUBBIO BASIN

17. 3D seismicresponse of the Gubbio basin • 17 Construction of the 3D SE model Deep geological model Layered - VS = 18003500 [m/s] x ~ 900 m at outcrop Alluvial basin x ~ 100 m VS(z) = 250 + 30z0.5 [m/s] linear-elastic Kinematic fault model from Hernandez et al. (2004)

18. 3D seismicresponse of the Gubbio basin Movie of velocity wavefield (FP component)

19. Comparison of 1D, 2D and 3D numerical results transverse comp. longitudinal comp.

20. 3D numerical simulations of the MW6.3 L’Aquila earthquake Paganica fault L’Aquila

21. L’Aquila AQU AQK AQM AQV AQG AQA 3D numerical simulations of the MW6.3 L’Aquila earthquake a Strong ground motion records in the epicentral area

22. 3D numerical simulations of the MW6.3 L’Aquila earthquake Near-fault acceleration records in L’Aquila Aterno river records L’Aquila downtown

23. 3D shape of the Aterno Valley based on recent geophysical surveys during microzonation studies linear-elastic soil behavior: AQK (~ 300 m) VS = 500+10z1/2 (m/s)  = 2000 (kg/m3) 3D numerical simulations of the MW6.3 L’Aquila earthquake Hexahedral SE mesh (fmax~ 2.5 Hz)

24. 3D numerical simulations of the MW6.3 L’Aquila earthquake Effect of stochastic source parameters Homogeneous kinematic parameters rise time = 0.9 s, rup. velocity = 2.5 km/s, rake = 255° slip distribution according to Walters et al. (2009) AQK AQK AQV AQV

25. slip rise time rup.vel rake • 25 3D numerical simulations of the MW6.3 L’Aquila earthquake Effect of stochastic source parameters Heterogeneous kinematic parameters, defined by spatially correlated stochastic fields for rise time, rup. velocity and rake angle, with correlation length 4 km AQK AQK AQV AQV

26. 26 3D numerical simulations of the MW6.3 L’Aquila earthquake

27. Model CM1 3D numerical simulations of the MW6.3 L’Aquila earthquake Comparison with observed MCS intensity Observed Simulated

28. Conclusions • 3D numerical simulations of earthquake ground motion in near-fault conditions, accounting for complex geological and morphological conditions, may provide realistic seismic scenarios, up to frequencies of 2 – 3 Hz. • The frequency limit is mainly related to insufficient details in the source kinematic models, as well as on the local geology description. A moderate random variability of the kinematic source parameters may significantly improve the high-frequency energy radiation, improving as well the agreement with observed records during L’Aquila earthquake. • The typical features of long period ground motion amplification and propagation of surface waves within sedimentary basins in Central Italy, such as in Gubbio, can be captured well by 3D numerical simulations. • Generation of realistic earthquake ground motion scenarios for future damaging earthquakes within complex tectonic and geological environments is becoming more and more feasible, also for engineering applications.

29. Thank you!