THESIS
2018
xxii, 178 pages : illustrations (some color) ; 30 cm
Abstract
Amplification of seismic waves due to surface topography and subsurface soils has often
been observed to cause intensive damage in past earthquakes. Understanding the topographic
amplification of ground motions can provide scientific guidelines for the design of buildings
and evaluation of regional scale landslide hazards in mountainous regions. This study aims to
numerically quantify the amplification of earthquake ground motions as well as the associated
landslide hazards due to 3D realistic topography and subsurface soil conditions. A series of
large-scale 3D numerical simulations are conducted to investigate the seismic topographic
amplification effect of Hong Kong Island using Spectral Element Method (SEM). The major
findings of this thesis are as follows:
(a) Parametric m...[
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Amplification of seismic waves due to surface topography and subsurface soils has often
been observed to cause intensive damage in past earthquakes. Understanding the topographic
amplification of ground motions can provide scientific guidelines for the design of buildings
and evaluation of regional scale landslide hazards in mountainous regions. This study aims to
numerically quantify the amplification of earthquake ground motions as well as the associated
landslide hazards due to 3D realistic topography and subsurface soil conditions. A series of
large-scale 3D numerical simulations are conducted to investigate the seismic topographic
amplification effect of Hong Kong Island using Spectral Element Method (SEM). The major
findings of this thesis are as follows:
(a) Parametric models for ground motion amplification considering 3D topography and
subsurface soils are developed. Results show that the topographic amplification factor
is frequency dependent, and the topographic amplification pattern is significantly
influenced by the thickness of the subsurface soil layer due to the coupled soil-topography
effect. The parametric models characterize the topographic amplification
considering subsurface soils, material damping and input wave frequencies using
simplified parameters such as smoothed curvature, slope angle, elevation and soil
depth. The predictions are proved to be accurate with standard deviation of residuals
generally between 0.1-0.15.
(b) Geostatistical method is proposed to construct 3D realistic subsurface soil profiles with
borehole data from field investigation. Variability of soil depths and the correlation
between the shear wave velocity and the SPT-N values is considered in this subsurface
soil velocity model. Ground motion simulations with the realistic subsurface soil
model show that the amplification factors are significantly large compared with rock
outcrop in the time and frequency domain. The amplification factor could reach as high
as more than 10 at some frequencies. If different sources of variabilities on soil profiles
are considered, the local amplification factor could become more variable. The
phenomenon is in line with large amplification factors observed in some case studies.
(c) The influence of heterogeneity of soils on the amplification effect of horizontally
layered soil grounds is quantified using 2D SEM analyses. Compared with a uniform
soil profile, soil heterogeneity, represented by spatially correlated random field, shifts
the resonance frequencies of the site and results in reduced amplification factors at high
frequencies. In general, spatially correlated random field with shorter correlation
distances behaves more homogeneously. Moreover, the spatial correlation distance of
the amplification factor at high frequencies is highly related to the horizontal
correlation distance of the spatially correlated random field.
(d) A physics-based method is proposed to evaluate the regional scale earthquake-induced
landslide hazards. The numerical simulation directly considers the amplification effect
of topography and soil layers, while the associated landslide is indicated by the
Newmark displacement analysis. Results show that the topographic amplification
effect and the vertical acceleration have a great impact on the results of Newmark
displacement analysis. Under the 2475-year-return-period earthquake, about 4.9% of
the terrain has a probability of slope failure of more than 5%. This physics-based
method can be performed as long as the topographic data, subsurface soil profiles are
provided and the seismic scenario is assumed.
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