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
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D earthquake ground motion numerical simulations
3
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
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D earthquake ground motion numerical simulations
4
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.
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D earthquake ground motion numerical simulations
Applications
5
seismic risk assessment of
urban areas under scenario
earthquakes
integration to PSHA, especially
for long return periods
seismic input for
strategic structures
- CyberShake (Graves et al., 2010)
PGV (cm/s)
ShakeOut Scenario: Southern
California (Tech. report, 2008)
- S2 Project DPC-INGV 2007-2009
(Faccioli et al, 2010)
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
3D earthquake ground motion numerical simulations
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
6
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 MW 6.3 2009 L’Aquila earthquake
 Conclusions
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
8
The Spectral Element 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
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
The Spectral Element code GeoELSE
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
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
L’Aquila basin
Dynamic response of structures
Seismic wave propagation in complex
geological configurations
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
11
The Spectral Element 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.
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
12
The Spectral Element code GeoELSE
 Spatial discretization
unstructured hexahedral SEsN = 2
N=3
N=4
 Numerical integration
Legendre-Gauss-Lobatto (LGL) rule
 Polynomial basis (test functions)
orthogonal Lagrange polynomials
of degree N (Spectral Degree)
N=4
 Time discretization:
explicit 2nd order FD (LF2-B2)
 Native implementation in parallel architectures
MPI (Message Passing Interface)
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
Treatment of seismic input in GeoELSE
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)
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 MW 6.3 2009 L’Aquila earthquake
 Conclusions
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
15
Case studies
Sedimentary basins in
Gubbio
Central Italy related to
extensional tectonic
activity
Rieti
Norcia
L’Aquila
Avezzano
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
Sulmona
POLITECNICO DI MILANO
3D seismic response of the Gubbio basin
16
The 1997-1998 Umbria Marche seismic sequence
GUBBIO
BASIN
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D seismic response of the Gubbio basin
Construction of the 3D SE model
17
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
SD
4
Kinematic fault model
from Hernandez et al.
(2004)
Elements Nodes
t
Duration fmax
#
#
(s)
(s)
(Hz)
361’752 ~ 23.5.106 3.4483·10-4
100
~2.5
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
CPU time (64)
(hours)
~ 84.6
POLITECNICO DI MILANO
3D seismic response of the Gubbio basin
18
Movie of velocity wavefield (FP component)
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
Comparison of 1D, 2D and 3D numerical results
transverse comp.
19
longitudinal comp.
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
20
Paganica fault
L’Aquila
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations
of the MW6.3 L’Aquila earthquake
a
21
Strong ground motion records in the epicentral area
L’Aquila
AQU
AQK
AQM
AQV
AQG
AQA
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
22
L’Aquila downtown
Aterno river records
Near-fault acceleration records in L’Aquila
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
23
Hexahedral SE mesh (fmax ~ 2.5 Hz)
3D shape of the Aterno Valley based on
recent geophysical surveys during
microzonation studies
linear-elastic soil behavior:
VS = 500+10z1/2 (m/s)
 = 2000
AQK (~ 300 m)
(kg/m3)
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
Effect of stochastic
source parameters
24
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
AQV
AQK
AQV
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
Effect of stochastic
source parameters
slip
rise time
rup.vel
25
rake
Heterogeneous kinematic
parameters, defined by
AQK
spatially correlated stochastic
fields for rise time, rup. velocity
and rake angle, with correlation
length 4 km
AQV
AQK
AQV
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
26
POLITECNICO DI MILANO
3D numerical simulations of the MW6.3 L’Aquila earthquake
27
Comparison with observed MCS intensity
Observed
Simulated
Model CM1
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
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.
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO
29
Thank you!
Roberto Paolucci: 3D numerical simulations of earthquake ground motion
POLITECNICO DI MILANO