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

Roberto Paolucci: 3D numerical simulations of earthquake ground motion 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 M W L’Aquila earthquake Conclusions

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 3 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 3D earthquake ground motion numerical simulations Objective

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 4 parametric studies on earthquake ground motion 3D earthquake ground motion numerical simulations Applications PGV maps in the Grenoble Valley due to a M w 6 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.

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

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 6 3D earthquake ground motion numerical simulations

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 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 M W L’Aquila earthquake Conclusions

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 8 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 Web site: The Spectral Element code GeoELSE

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 9 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 The Spectral Element code GeoELSE

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 10 The Spectral Element code GeoELSE Dynamic Soil Structure Interaction Traffic-induced vibrations Dynamic response of structures Seismic wave propagation in complex geological configurations L’Aquila basin

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 11 Kosloff D, Baysal E. Forward modelling by the Fourier method Geophysics : 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: 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; 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: Some “historical” references on spectral approaches for the numerical integration of the wave equation The Spectral Element code GeoELSE

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 12 Spatial discretization unstructured hexahedral SEs Numerical integration Legendre-Gauss-Lobatto (LGL) rule Polynomial basis (test functions) orthogonal Lagrange polynomials of degree N (Spectral Degree) Time discretization: explicit 2 nd order FD (LF2-B2) Native implementation in parallel architectures MPI ( Message Passing Interface ) N = 4 The Spectral Element code GeoELSE

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 13 plane wave incidence with arbitrary angles (engineering applications) kinematic modeling of a seismic fault with spatially varying source parameters (seismic hazard evaluations, seismic scenarios) Treatment of seismic input in GeoELSE

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 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 M W L’Aquila earthquake Conclusions

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 15 Sedimentary basins in Central Italy related to extensional tectonic activity Case studies Rieti Avezzano Sulmona L’Aquila Norcia Gubbio

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO GUBBIO BASIN 16 The Umbria Marche seismic sequence 3D seismic response of the Gubbio basin

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 17 Construction of the 3D SE model SD Elements # Nodes #  t (s) Duration (s) f max (Hz) CPU time (64) (hours) 4361’752~ · ~2.5 ~ 84.6 Deep geological model Layered - V S = 1800  3500 [m/s]  x ~ 900 m at outcrop Alluvial basin  x ~ 100 m V S (z) = z 0.5 [m/s] linear-elastic Kinematic fault model from Hernandez et al. (2004) 3D seismic response of the Gubbio basin

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 18 Movie of velocity wavefield (FP component) 3D seismic response of the Gubbio basin

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 19 Comparison of 1D, 2D and 3D numerical results transverse comp. longitudinal comp.

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 20 L’Aquila Paganica fault 3D numerical simulations of the M W 6.3 L’Aquila earthquake

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 21 a 3D numerical simulations of the M W 6.3 L’Aquila earthquake L’Aquila AQM AQK AQV AQA AQG AQU Strong ground motion records in the epicentral area

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 22 Near-fault acceleration records in L’Aquila Aterno river records L’Aquila downtown 3D numerical simulations of the M W 6.3 L’Aquila earthquake

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 23 AQK (~ 300 m) linear-elastic soil behavior: V S = z 1/2 (m/s)  = 2000 (kg/m 3 ) 3D shape of the Aterno Valley based on recent geophysical surveys during microzonation studies Hexahedral SE mesh ( f max ~ 2.5 Hz) 3D numerical simulations of the M W 6.3 L’Aquila earthquake

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 24 AQK AQV Homogeneous kinematic parameters rise time = 0.9 s, rup. velocity = 2.5 km/s, rake = 255° slip distribution according to Walters et al. (2009) Effect of stochastic source parameters 3D numerical simulations of the M W 6.3 L’Aquila earthquake AQK AQV

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO Heterogeneous kinematic parameters, defined by spatially correlated stochastic fields for rise time, rup. velocity and rake angle, with correlation length 4 km Effect of stochastic source parameters 25 AQK AQV 3D numerical simulations of the M W 6.3 L’Aquila earthquake AQK AQV slip rise time rup.vel rake

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 26 3D numerical simulations of the M W 6.3 L’Aquila earthquake

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 27 Observed Simulated Comparison with observed MCS intensity Model CM1 3D numerical simulations of the M W 6.3 L’Aquila earthquake

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 28 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. Conclusions

Roberto Paolucci: 3D numerical simulations of earthquake ground motion POLITECNICO DI MILANO 29 Thank you!