3D PHYSICS-BASED NUMERICAL SIMULATIONS: ADVANTAGES AND LIMITATIONS OF A NEW FRONTIER TO EARTHQUAKE GROUND MOTION PREDICTION.

Transcription

1 6th National Conference on Earthquake Engineering & 2nd National Conference on Earthquake Engineering and Seismology June 14-16, D PHYSICS-BASED NUMERICAL SIMULATIONS: ADVANTAGES AND LIMITATIONS OF A NEW FRONTIER TO EARTHQUAKE GROUND MOTION PREDICTION Department of Civil and Environmental Engineering, Politecnico di Milano Contents 2 Motivation for 3D physics-based earthquake ground motion simulations the spectral element code SPEED 3D physics-based earthquake ground motion simulations in Istanbul producing broadband ground motions 1

2 Approaches to earthquake ground motion prediction 3 Physics-based Limitations in the use of GMPEs 4 range of potential damage to structures NGA West2 database (Ancheta et al., 2013) 2

3 Limitations in the use of GMPEs 5 Limitations in the use of GMPEs 6 3

4 Limitations in the use of GMPEs 7 NGA2 records M>6 R<20km Limitations in the use of GMPEs 8 INGV wordlwide near source dataset 6 < M < 7 & PGA > 100 cm/s2 4

5 Physics-based 3D earthquake ground motion simulations 9 Objective To create a numerical laboratory to simulate earthquake ground shaking scenarios 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 and of resulting ground motion Physics-based 3D earthquake ground motion simulations 10 GMPEs 3D physics based GM simulations but you need 3D numerical models high frequency verifications on real earthquakes 5

6 Contents 11 Motivation for 3D physics-based earthquake ground motion simulations the spectral element code SPEED 3D physics-based earthquake ground motion simulations in Istanbul producing broadband ground motions SPEED (speed.mox.polimi.it) 12 6

7 SPEED: some references 13 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 Stupazzini M., Paolucci R., Igel H. Near-fault earthquake ground motion simulation in the Grenoble Valley by a highperformance spectral element code Bulletin of the Seismological Society of America, 2009 Mazzieri I., Stupazzini M., Guidotti R., Smerzini C. SPEED-Spectral Elements in Elastodynamics with Discontinous Galerkin. A nonconforming approach for 3D multi-scale problems. International Journal for Numerical Methods in Engineering, 2013 SPEED: main features 14 Features 3D unstructured conforming and nonconforming hexahedral meshes ( e.g., between sub-domains Ω 1,2, Ω 3 and Ω 4 ) Non uniform polynomial approximation orders (e.g., between sub-domains Ω 1 and Ω 2 ) leap-frog FD time advancing scheme visco-elastic and non-linear elastic soil behaviour Kernel hybrid parallel programming based on MPI and Open-MP METIS software library to handle partitioning and load balancing designed for multi-core machines or large clusters - optimized for HPC clusters (e.g., FERMI Blugene/Q) 7

8 SPEED: spatial discretization 15 Legendre-Gauss-Lobatto points Lagrange polynomials SPEED: Treatment of seismic input 16 Kinematic modeling of an extended seismic source m k k M 0 ij ( x, t) k volume of the k th subfault M k 0 k (x, t) u shear modulus (x, t) k k i n j j n i V k area k k k A s( t t ; ) co-seismic slip R slip and normal fault vectors f( f, f, f ) Slip source function How to introduce high-frequency components? How to introduce spatial incoherency? 8

9 SPEED: soil modelling 17 Non-linear elasticity sand clay Viscoelastic models Q = cost Q=Q 0 f Rayleigh damping Previous applications of SPEED (1) 18 Stupazzini M, Paolucci R, Igel H (2009) Near-fault earthquake ground-motion simulation in the Grenoble valley by a high-performance Spectral Element code. BSSA, 99: Smerzini C, Villani M (2012) Broadband numerical simulations in complex near field geological configurations: the case of the M W L'Aquila earthquake, BSSA, 102:

10 Previous applications of SPEED (2) 19 Gubbio (Central Italy) Sulmona (Central Italy) Santiago de Chile Christchurch earthquake February 22, 2011 (New Zealand) Wellington (New Zealand) Po Plain earthquake May 29, 2012 (Northern Italy) Marsica earthquake 1915 (Central Italy) Thessaloniki (Greece) Istanbul (Turkey) Beijing (China) Contents 20 Motivation for 3D physics-based earthquake ground motion simulations the spectral element code SPEED 3D physics-based earthquake ground motion simulations in Istanbul producing broadband ground motions 10

11 Past century earthquakes along the North Anatolian Fault 21 after Bohnhoff et al., 2013 Princes Islands segment of the NAF 22 Yellow stars mark estimated epicentres of major earthquakes along the Princes Islands segment during the last 2,000 years. After Bohnhoff et al.,

12 Setup of the 3D physics-based numerical simulations 23 Construction of the numerical model (1) 24 Combined digital elevation/bathimetry model 12

13 Construction of the numerical model (2) 25 Vs model Construction of the numerical model (3) 26 Fault geometry model 13

14 Construction of the numerical model (4) 27 Spectral element numerical model (resolution: f max = 1.5 Hz) Slip distribution along the fault 28 Kinematic slip distribution models HB94: Herrero and Bernard (1994) CA15: Crempien and Archuleta (2015) 14

15 Construction of scenario earthquakes scenario earthquakes of M ranging from 7 to 7.4 where constructed by considering randomly generated hypocenter and slip distribution models, with both HB94 and CA15 approaches Post-processing 45 shaking scenarios (7.0 M w 7.4) 30 Comparison of M w 7 scenarios: effect of directivity Forward directivity PGV (cm/s) Neutral directivity PGV (cm/s) Backward Scen Antidirective directivitypgv (cm/s) 15

16 Post-processing 45 shaking scenarios (7.0 M w 7.4) 31 Ground motions for a selected scenario Post-processing 45 shaking scenarios (7.0 M w 7.4) 32 Ground motions for a selected site 16

17 Post-processing 45 shaking scenarios (7.0 M w 7.4) 33 Animation of ground motion: effect of directivity Neutral Forward Backward Dependendance of results on ruptured segments 34 when 3 segments are ruptured, the FW directivity scenario wrt Istanbul is the most likely to occur 17

18 Comparison with GMPEs 35 Chiou and Youngs (2008) Bray & Rodriguez-Marek (2004) only FW directivity Comparison with GMPEs 36 Chiou and Youngs (2008) Bray & Rodriguez-Marek (2004) only FW directivity 18

19 Components of single-station standard deviation 37 records of Christchurch earthquakes (Chen and Faccioli, 2013) total s.d. within-event s.d. between-event s.d. Contents 38 Motivation for 3D physics-based earthquake ground motion simulations the spectral element code SPEED 3D physics-based earthquake ground motion simulations in Istanbul producing broadband ground motions 19

20 Producing broadbands from SPEED 39 (1) A hybrid broadband is first produced by combining the low-frequency simulation with the high-frequency ground motion generated from stochastic approaches FAS (cm/s) LF filter f l f (Hz) LF(SPEED) HF(SP96) BB f h 10 0 f (Hz) HF filter LF (cm/s 2 ) HF (cm/s 2 ) BB (cm/s 2 ) LF: SPEED (f < 1.5 Hz) HF: SP96 (f > 1.5 Hz) BB ( 0 < f < 25 Hz) t (s) lack of correlation of the LF and HF parts Producing broadbands from SPEED 40 (2) An ANN is trained (una tantum) based on a strong motion dataset (SIMBAD, Smerzini et al., 2014) 20

21 Producing broadbands from SPEED 41 (3) The "hybrid" broadband is scaled in order to match the ANN trained response spectrum hybrid Sa hybrid response spectrum region of validity of numerical simulations ANN-matched ANN response spectrum 3D physics-based simulated response spectrum T* T Producing broadbands from SPEED 42 (4) Verification on real case studies: simulation of Po Plain eqk, May rec acceleration sim acceleration rec velocity sim velocity response spectra Fourier spectra 21

22 Producing broadbands from SPEED 43 (4) Verification on real case studies: simulation of Po Plain eqk, May Spatial correlation of PGAs recorded simulated Producing broadbands from SPEED 44 (4) Verification on real case studies: simulation of Po Plain eqk, May Spatial correlation of Sa=1s recorded simulated 22

23 45 3D numerical simulations of the May Po Plain earthquake 46 3D numerical simulations of the May Po Plain earthquake 23

24 Producing ground motion movies: 2012 Po Plain eqk 47 Conclusions 48 Pros accounting for specific geologic and tectonic conditions capturing physics of earthquake ground motion, especially near-source proper spatial correlation of motion between adjacent sites Cons large number of scenarios needed: how to cluster them? limited reliability in the high-frequency range, although in progress need of vast amount of input data: suitable for large urban areas 24

25 Acknowledgements 49 Munich Re (Germany) "3D physics-based earthquake ground shaking scenarios in large urban areas" Reluis (Italy) RS2 Project : "3D numerical simulations and near-source effects" 25