  Local wave amplification due to strong seismic motions in surficial
multilayered soil is influenced by several parameters such as the wavefield
polarization and the dynamic properties and impedance contrast between soil
layers. The present research aims at investigating seismic motion amplification
in the 2011 Tohoku earthquake through a one-directional three-component (1D-3C)
wave propagation model. A 3D nonlinear constitutive relation for dry soils
under cyclic loading is implemented in a quadratic line finite element model.
The soil rheology is modeled by mean of a multi-surface cyclic plasticity model
of the Masing-Prandtl-Ishlinskii-Iwan (MPII) type. Its major advantage is that
the rheology is characterized by few commonly measured parameters. Ground
motions are computed at the surface of soil profiles in the Tohoku area (Japan)
by propagating 3C signals recorded at rock outcrops, during the 2011 Tohoku
earthquake. Computed surface ground motions are compared to the Tohoku
earthquake records at alluvial sites and the reliability of the 1D-3C model is
corroborated. The 1D-3C approach is compared with the combination of three
separate one-directional analyses of one motion component propagated
independently (1D-1C approach). The 3D loading path due to the 3C-polarization
leads to multiaxial stress interaction that reduces soil strength and increases
nonlinear effects. Time histories and spectral amplitudes, for the Tohoku
earthquake, are numerically reproduced. The 1D-3C approach allows the
evaluation of various parameters of the 3C motion and 3D stress and strain
evolution all over the soil profile.
