Abstract
In this paper, considering the far-field seismic input, an accelerogram recorded in the bedrock at Wuquan Mountain in Lanzhou city during the 2008 Wenchuan Ms8.0 earthquake was selected, and numerical dynamic analyses were conducted. The one-dimensional equivalent linear method was implemented to estimate the ground motion effects in the loess regions. Thereafter, slope topographic effects on ground motion were studied by applying the dynamic finite-element method. The results revealed the relationship between the PGA amplification coefficients and the soil layer thickness, which confirmed that the dynamic response of the sites had obvious nonlinear characteristics. The results also showed that there was an obvious difference in the dynamic magnification factor between the short-period and long-period structures. Moreover, it was found that the amplification coefficient of the observation point at the free surface was greater than the point inside the soil at the same depth, which mainly occurred in the upper slope. Through this study, the quantitative assessment of ground motion effects in loess regions can be approximately estimated, and the amplification mechanism of the far-field ground motion mechanism can be further explained. In addition to the refraction and reflection theory of seismic waves, the resonance phenomenon may help explain the slope topographic effect through spectrum analysis.
Highlights
Loess and loessic deposits account for approximately 6.63% of the total area of China
Together with the impressive features of geomorphology and deposit thickness, seismic damage becomes more serious in the loess areas than in nonloessic areas [2]
Earthquake damage investigation in loess areas shows that the earthquake disaster characteristics are closely related to topography, lithology, geological structure, deposit thicknesses, etc
Summary
Loess and loessic deposits account for approximately 6.63% of the total area of China. Through the above analysis and discussion, the amplification effects of soil sites on ground motions were presented On this basis, slope topographic effects on ground motion were studied by applying the nonlinear dynamic finite element analysis method, and the kinetic equation of the soil seismic response can be expressed as:. The dominant frequency of ground motion on the top of the slope is 1.9 Hz, while this values is below 1 Hz. Fig 11 illustrates the acceleration time histories and the spectrum characteristics at the free surface with different slope heights. It is further shown that the amplification of the peak ground acceleration mainly occurs in the upper slope, ranging in height from 40 to 50 meters
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