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Research and teaching activities of Jean-François Semblat
Laboratoire Central des Ponts et Chaussées, Paris, France, semblat_at_lcpc.fr (at=@)
Teaching :

Ecole Polytechnique (Mechanics of continua, Seismology and tectonics)

ENTPE (Numerical methods)

University Pierre & Marie Curie (Dynamics of solids)

Rose School (Advanced Computational Methods)
Publications :

New book “Waves and Vibrations in Soils:
Earthquakes, Traffic, Shocks, Construction
Works” (IUSS Press, 2009)
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Short list

Recent publications (author version):
http://hal.archives-ouvertes.fr/aut/semblat/
Researches :
Propagation and amplification of seismic waves.
Mechanical and numerical modeling.
1
Amplification of seismic waves in alluvial basins
The amplification of seismic waves at the free surface, namely « site effects » [1], may strengthen the
impact of an earthquake in specific areas (e.g. Mexico 1985). Indeed, when seismic waves propagate
through alluvial layers or scatter on strong topographic irregularities, refraction/scattering phenomena
may strongly increase the amplitude of the ground motion. It is then possible to observe stronger motions
further away from the epicenter !
At the scale of an alluvial basin, the analysis of seismic wave propagation is a complex problem
involving as various phenomena as : resonance of the whole basin [2], propagation in heterogeneous
media [3], generation of surface waves on the basin edges [5], nonlinear behaviour of geomaterials [6].
1.1
Simplified modal approach: characterization of the fundamental frequency
Site effects can then be analyzed as a global
resonance of alluvial basins. Simplified modal
approaches, based on the Rayleigh approximation,
have been considered [2]. Starting from admissible 2D
or 3D eigenmodes, these approaches allow a fast and
reliable estimation of the fundamental frequency of
geological structures [2].
Basin fundamental frequency by modal approach >
1.2
Propagative approaches through the Boundary Element Method
Previous approaches do not allow a quantitative estimation of the amplification level of seismic waves
and it is then necessary to simulate numerically their propagation.
Various numerical methods are available: finite
differences, finite elements [6], boundary elements
[5,7], spectral elements, etc. At the scale of an
alluvial basin, the amplification of seismic waves in
surficial layers is analyzed using the Boundary
Element Method for the site of Volvi, Nice and
Caracas [4,5,7]. The geometrical irregularities
(topography) and the velocity heterogeneities
(lithology) have a significant influence on the
amplification
process.
Comparisons
between
numerical and experimental results, measured for
weak earthquakes, are obvious evidences of such
phenomena [5,8]. A new "fast multipole" formulation
for boundary integral equations in elastodynamics
has recently allowed an important reduction of the
computational cost as well as the memory
requirements [9,10].
Seismic wave amplification in Nice [5]
Seismic wave amplification in Volvi [4].
Seismic wave amplification in Caracas [8]
Fast Multipole Method : semi-spherical canyon [9]
Fast Multipole Method : semi-spherical canyon [10]
1.3
Amplification of strong earthquakes: simplified nonlinear model
In the case of strong seismic motion, the influence of the constitutive nonlinearities in surficial layers is
significant. A simplified nonlinear model (nonlinear viscoelasticity) has been developed to take
simultaneously into account, for increasing shear strain, the shear modulus reduction and the increase of
the energy dissipation [6]. The one-dimensional simulations performed with this simplified model lead to
lower amplitudes, larger propagation delays and the generation of odd order harmonics. These results
are in good agreement with the experimental observations (e.g. comparisons with surface and in-depth
recordings for the Kushiro-Oki earthquake [6]).
Nonlinear attenuation model for strong motions [6]
2
Simulations for Kushiro-Oki earthquake [6]
Interaction of seismic waves with a dense building array
The surface structures may act as secondary seismic sources and modify the seismic "free-field" [11].
Considering experimental results obtained from the Volvi European test site, the numerical modeling of
structure-soil-structure interaction allows the determination of the parameters governing these
interactions. At large scales, the interaction between an alluvial basin and a building network – or site-city
interaction - is analyzed numerically [12]. The coincidence between the eigen frequencies of the
structures and the fundamental frequency of the basin strongly influences the site-city interaction. The
coherency of the wavefield, the effects of the urban density and the building heterogeneity have also
been studied.
Structure-soil interaction (Volvi EuroSeisTest) [11]
Site-city interaction in an alluvial basin [12,13]
References
[1] Semblat J.F., B.Gatmiri, P.Y.Bard, P.Delage (2006). Séisme en ville, La Recherche, 398 : 29-31.
[2] Semblat J.F., R.Paolucci, A.M.Duval (2003). Simplified vibratory characterization of alluvial basins, C. R.
Geoscience, 33(4): 365-370.
[3] Abraham O., R.Chammas, P.Cote, H.Pedersen, J.F.Semblat (2004). Mechanical characterization of
heterogeneous soils with surface waves, Near Surface Geophysics, 2: 249-258.
[4] Semblat J.F., Duval A.M., Dangla P. (2000). Numerical analysis of seismic wave amplification in Nice (France)
and comparisons with experiments, Soil Dynamics and Earthquake Engineering, 19(5), pp.347-362.
[5] Semblat J.F., M.Kham, E.Parara, P.Y.Bard, K.Pitilakis, K.Makra, D.Raptakis (2005). Site effects : basin geometry
vs soil layering, Soil Dynamics and Earthquake Eng., 25(7-10): 529-538.
[6] Delépine N., Bonnet G., Semblat J-F, Lenti L. (2007). A simplified non linear model to analyze site effects in
alluvial deposits, 4th Int. Conf. on Earthquake Geotechnical Eng., Thessaloniki, Greece, June 25-28.
[7] Dangla P., J.F.Semblat, H.Xiao, N.Delépine (2005). A simple and efficient regularization method for 3D BEM:
application to frequency-domain elastodynamics, Bull. of the Seismological Soc. of America, 95(5): 1916-1927.
[8] Semblat J.F., Duval A.M., Dangla P. (2002). Seismic Site Effects in a Deep Alluvial Basin: Numerical Analysis by
the boundary element method, Computers and Geotechnics, 29(7): 573-585.
[9] Chaillat S., Bonnet M., Semblat J-F (2008). A multi-level Fast Multipole BEM for 3-D elastodynamics in the
frequency domain, Computer Methods in Applied Mechanics and Engineering, 197(49-50), pp.4233-4249.
[10] Chaillat S., Bonnet M., Semblat J-F (2009). A new fast multi-domain BEM to model seismic wave propagation
and amplification in 3D geological structures, Geophysical Journal International (to appear).
[11] Bard P.Y., J.L.Chazelas, P. Guéguen, M. Kham, J.F. Semblat (2005). Assessing and managing earthquake risk Chap.5 : Site-city interaction, Eds: C.S. Oliveira, A. Roca and X. Goula, Springer, 375 pages.
[12] Kham M., J.F. Semblat, P.Y.Bard, P.Dangla (2006). Site-City Interaction: main governing phenomena through
simplified numerical models, Bulletin of the Seismological Society of America, 96(5): 1934-1951.
[13] Semblat J.F., Kham M., Bard P.Y. (2008). Seismic Site Effects in Alluvial Basins and Influence of Site-City
Interaction, Bulletin of the Seismological Society of America, 98(6), pp.2665-2678, 2008.
[14] Semblat J.F., Pecker A. (2009). Waves and Vibrations in Soils: Earthquakes, Traffic, Shocks, Construction
Works, IUSS Press, 500 pages.