Strong Ground Motion in the 2011 Tohoku Earthquake: a 1Directional - 3Component Modeling

TL;DR

This study models seismic wave amplification during the 2011 Tohoku earthquake using a 1D-3C wave propagation approach with nonlinear soil rheology, accurately reproducing observed ground motions and highlighting the importance of 3C effects.

Contribution

The paper introduces a novel 1D-3C modeling framework incorporating a multi-surface cyclic plasticity soil model, improving the simulation of complex 3C seismic motions in layered soils.

Findings

The 1D-3C model accurately reproduces observed ground motions.

3C polarization effects significantly influence soil stress and nonlinear response.

The approach provides detailed insights into 3D stress-strain evolution during earthquakes.

Abstract

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.