Earthquakes
are one of the most significant destructing natural hazards affecting a large
population worldwide. For this reason, ground motion predictions are critical
to evaluate the seismic hazard in highly populated areas, which in some cases,
are located on site conditions prone to seismic amplification. Soil
amplification is one of the most important factors affecting the earthquake
ground motion. When the incident wave field is strong enough and the soil
strength is relatively weak, nonlinear material behavior appears, introducing
important changes such as soil degradation, and if the material is granular and
water saturated, cyclic mobility and liquefaction. In this work, I study the
numerical modeling of wave propagation in 1D/2D complex media that include
nonlinear soil behavior under the framework of the spectral element method
(SEM). The consideration of soil nonlinearity holds an important place in order
to achieve simulations consistent with real observations for strong seismic shaking.
Additionally, in the presence of strong ground motion in saturated soils, pore pressure
becomes an important parameter to take into account for related phenomena such
as flow liquefaction and cyclic mobility. In this study, first, one component
(1C) - seismic wave propagation is modeled in linear and nonlinear media in 1D
based on the spectral element numerical method. Viscoelastic and nonlinear soil
rheologies are implemented by use of the memory variables technique and Iwan’s
elastoplastic model, respectively. Then, the same study is extended to a 1D -
three component (3C) model and a preliminary comparison on the effect of using
1C and 3C approaches is made. Then, the influence of excess pore pressure development
is included in the 1D-3C model and the developed numerical model is applied to
realistic case on the site of Wildlife Refuge Liquefaction Array (USA) which is
affected by the 1987 Superstition Hills event. The ground motion modification
for different assumptions of the soil rheology in the media and different input
motions is studied. The calculated motion is found to be amplified on low
frequency and damped in high frequency range due to excess pore pressure
development. Furthermore, the soil is found to be more nonlinear under triaxial
loading in 3C approach and more dilatant due to higher nonlinearity. Despite
the similitude in surface acceleration and velocity results, significant
differences in surface displacement results of 1C and 3C approaches are
remarked. Similar analyses are performed on two Japanese sites Kushiro Port and
Onahama Port, which are influenced by the 1993 Kushiro-Oki and the 2011 off the
Pacific coast of Tohoku earthquakes, respectively. It has been shown that the nonlinearity-related
changes are not homogeneous all over the concerned frequency band and the
influence of cohesionless soil behavior on wave propagation is highly dependent
on model properties and loading conditions. Lastly, the 2D SEM code is
developed by taking into account soil nonlinearity and pore pressure effects
similarly to 1D-3C SEM code. The developed 2D SEM code is applied to a 2D
sedimentary basin site where the basin geometry is asymmetrical and soil
profile consists of layers with different nonlinearity properties. P-SV and SH
2D wave propagation considering dry (total stress) and saturated (effective
stress) soil conditions are performed. The calculated surface motion differs
significantly as a function of the input motion loading conditions and the
resultant deformation in superficial layers can be very high in effective
stress analysis compared to total stress analysis. Furthermore, material
nonlinearity is traduced by a reduction of the seismic wave speed making wave propagation
takes longer time inside basin media and the reflections on bedrock-basin
boundaries lead the soil in basin edges to higher nonlinearity. This study
shows the possibility of modeling nonlinear soil behavior including pore
pressure effects in seismic wave propagation studies by coupling different
models with spectral element method. These analyses help identifying and
understanding dominant phenomena occurring in superficial layers, depending on
local conditions and input motions. This is of great importance for
site-specific studies.