roberto paolucci

3D NUMERICAL SIMULATIONS OF EARTHQUAKE GROUND 3D NUMERICAL SIMULATIONS OF EARTHQUAKE GROUND MOTION IN SEDIMENTARY BASINS: THE CASES OF MOTION IN SEDIMENTARY BASINS: THE CASES OF

GUBBIO AND L’AQUILA, CENTRAL ITALYGUBBIO 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

2ContentsContents

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

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 simulations3D earthquake ground motion numerical simulations

Objective


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parametric studies on earthquake ground motion


Applications

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.


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integration to PSHA, especially for long return periods

- CyberShake (Graves et al., 2010)

- S2 Project DPC-INGV 2007-2009 (Faccioli et al, 2010)

seismic risk assessment of urban areas under scenario

earthquakes

ShakeOut Scenario: Southern California (Tech. report, 2008)

PGV (cm/s)


Applications

seismic input for strategic structures

after the Japanese guidelines for evaluation of seismic hazard for nuclear installations (IAEA, 2010)


7ContentsContents



Case studies



Conclusions


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: http://geoelse.stru.polimi.it

The Spectral Element code The Spectral Element code GeoELSEGeoELSE


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Main purpose of GeoELSEStudying 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



10The Spectral Element code The Spectral Element code GeoELSEGeoELSE

Dynamic Soil Structure Interaction Traffic-induced vibrations

Dynamic response of structures Seismic wave propagation in complex geological configurations

L’Aquila basin


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Kosloff D, Baysal E. Forward modelling by the Fourier methodGeophysics 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 methodJournal 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.

Some “historical” references on spectral approaches for the numerical integration of the wave equation



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Spatial discretizationunstructured hexahedral SEs

Numerical integrationLegendre-Gauss-Lobatto (LGL) rule

Polynomial basis (test functions)orthogonal Lagrange polynomials of degree N (Spectral Degree)

Time discretization: explicit 2nd order FD (LF2-B2)

Native implementation in parallel architectures MPI (Message Passing Interface)

N = 4



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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 Treatment of seismic input in GeoELSEGeoELSE


14ContentsContents



Case studies



Conclusions


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Sedimentary basins in

Central Italy related to

extensional tectonic

activity

Case studiesCase studies

Rieti

Avezzano

Sulmona

L’Aquila

Norcia

Gubbio


GUBBIO GUBBIO BASINBASIN

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The 1997-1998 Umbria Marche seismic sequence

3D seismic response of the Gubbio basin3D seismic response of the Gubbio basin


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Construction of the 3D SE model

SD Elements#

Nodes#

t(s)

Duration (s)

fmax (Hz)

CPU time (64)(hours)

4 361’752 ~ 23.5.106 3.4483·10-4 100 ~2.5 ~ 84.6

Deep geological modelLayered - VS = 18003500 [m/s]x ~ 900 m at outcrop

Alluvial basin x ~ 100 mVS(z) = 250 + 30z0.5 [m/s] linear-elastic Kinematic fault model

from Hernandez et al. (2004)



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Movie of velocity wavefield (FP component)



19Comparison of 1D, 2D and 3D numerical results Comparison of 1D, 2D and 3D numerical results

transverse comp. longitudinal comp.


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L’AquilaPaganica fault

3D numerical simulations of the M3D numerical simulations of the MWW6.3 L6.3 L’’Aquila earthquake Aquila earthquake


21a3D numerical simulations of the M3D numerical simulations of the MWW6.3 L6.3 L’’Aquila earthquake Aquila earthquake

L’Aquila

AQM

AQK

AQV

AQA

AQG

AQU

Strong ground motion records in the epicentral area


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Near-fault acceleration records in L’Aquila

Ate

rno

river

reco

rds

L’A

quila

dow

ntow

n



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AQK (~ 300 m)linear-elastic soil behavior:VS = 500+10z1/2 (m/s)

= 2000 (kg/m3)

3D shape of the Aterno Valley based on recent geophysical surveys during microzonation studies

Hexahedral SE mesh (fmax ~ 2.5 Hz)



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AQK

AQV

Homogeneous kinematic parametersrise 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


AQK

AQV


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

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AQK

AQV


AQK

AQV

slip rise time rup.vel rake


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Observed Simulated

Comparison with observed MCS intensity

Model CM1



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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 Conclusions


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Thank you!Thank you!

roberto paolucci

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