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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. Contents.

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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

slide2

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
slide3

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
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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.

slide5

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)

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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
slide8

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
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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

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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

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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.
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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)

slide13

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)
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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
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Case studies

Sedimentary basins in Central Italy related to extensional tectonic activity

Gubbio

Norcia

Rieti

L’Aquila

Avezzano

Sulmona

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3D seismicresponse of the Gubbio basin

The 1997-1998 Umbria Marche seismic sequence

GUBBIO BASIN

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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)

slide18

3D seismicresponse of the Gubbio basin

Movie of velocity wavefield (FP component)

slide19

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

transverse comp.

longitudinal comp.

slide21

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

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

Near-fault acceleration records in L’Aquila

Aterno river records

L’Aquila downtown

slide23

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)

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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

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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

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26

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

slide27

Model CM1

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

Comparison with observed MCS intensity

Observed

Simulated

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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.
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