| Numerical simulation of low-frequency ground motion is an important method to study and analyze the damage of building structures under seismic waves.In the past decades,a large number of long-period structures(oil tanks,long bridges,etc.)have been seriously damaged in earthquakes,and the damage is caused by low-frequency ground motions.The low-frequency ground motion numerical simulation is conducive to reducing the disasters caused by ground motions in the future,and provide some reference for earthquake prevention and disaster reduction,and also provide data parameters for large-scale engineering structure design.In this paper,the low-frequency ground motions of 2013 Mw 6.6 Lushan earthquake is simulated by the finite-difference method.Considering the uncertainty of the rupture starting point,the low-frequency ground motion is derived by analogy with the electron cloud model of the ground state hydrogen atom.The final simulated waveforms are compared with the actual observation records.In order to further consider the uncertainty of source parameters in the numerical simulation of ground motions,the Nanyuan-Tongxian fault in Beijing is selected as the research object.By considering the uncertainty of asperity parameters and fracture modes,24 source models with magnitude of Mw6.5 are established to simulate the low-frequency ground motions of NanyuanTongxian fault.The simulations provide a certain reference for regional seismic fortification.The main research contents and conclusions of this paper are as follows:(1)Taking the 2013 Mw 6.6 Lushan earthquake as an example by using the finite-difference method.Based on the existing research results,a source model of the rupture starting point analogous to the electron cloud model is established.Combining the probability of the electron cloud model,the simulation results are obtained by superposition.Comparing the simulation results with the station records,it is found that the velocity waveforms and velocity response spectrums are in good agreement.It is proved that it is feasible to consider the uncertainty of the rupture starting point through the electron cloud model.(2)Considering the uncertainty of the rupture starting point,the simulation results will be different in the case of a single variable.The change of peak velocity is closely related to the rupture starting point,and the ground motion has great temporal and spatial distribution differences.The rupture starting point in some areas can produce greater ground motion.It shows that the uncertain factors have an important influence on the numerical simulation of ground motion.Due to the coupling effect of the hanging wall effect,directivity effect,and topographic effect,the ground motion distribution is uneven,and the ground motion of the hanging wall side is large.Under different source parameters,the expression of each effect also has strong differences.(3)In order to analyze the characteristics of ground motions in the study area,using the method of setting earthquake,24 different source models are used to simulate long-period ground motions of Nanyuan-Tongxian fault in Beijing.The results show that the difference of source parameters has a significant influence on the ground motion distribution.The intensity in the nearfield can exceed Ⅶ and the ground motions attenuate slowly in the strike direction.The maximum peak velocities are mostly distributed in the range of the fault distance of about 10km.(4)In Beijing area,due to the hanging wall effect,the hanging wall regions of Shunyi,Changping,Chaoyang,Dongcheng District,etc.will produce large ground motions under the bilateral fracture mode and the unilateral fracture mode.The intensity in this area can reach above grade Ⅵ,and will suffer great risks when the earthquake occurs,and some old buildings may be damaged. |
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