The Effect Analysis of Topography on the Spectrum Property of Ground Motion

Abstract eng:
This paper presents results of numerical analyses for the seismic response of uniform visco-elastic site under different vertically propagating seismic waves including SH waves、SV waves and P waves. The aim of this paper is to explore the effects of site geometry, dynamic properties of soil or rock, as well as predominant excitation frequency on seismic ground motion. A step-like slope model and a mesa model are established and an explicit finite difference method is performed to evaluate the significance of topography effects. Two-dimensional finite-element analyses are conducted using artificial bell-shape impulse wavelets and recorded bedrock motions as base excitation. Moreover, effects of slope inclination、the incident direction and characteristic size of step-like slope on the spectrum property of the incoming waves are all discussed in detail. The conclusions show that the presence of topographic factors and the direction of the incident waves not only significantly affect the peak ground acceleration of sites, but also affect the spectrum property of the incoming waves, and the effect of direction of the incident waves is especially remarkable. The study also finds that it is reasonable to analysis spectrum properties with the input of impulse wavelets in the finite element simulation of wave motion. Furthermore, the spectrum ratio defined in this paper can be more effectively used to extract the pure effect of topographic irregularities compared with transfer function which is also widely adopted.

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