Research On Characteristics Of Ground Motion Amplification In Two-dimensional Layered Basins Under Plane Wave Incidence

Several earthquake damage examples show that the basin site has a significant amplification effect on ground motion.Basin effect,as a typical representative of site seismic effect research,is of great significance in the fields of quantitative estimation of ground motion,site selection and seismic design of major projects and important buildings,seismic zoning and so on.In this paper,based on the two-dimensional layered basin model and the results of one-dimensional equivalent soil layer model corresponding to different field points in the basin,a large number of two-dimensional and one-dimensional model calculation examples are carried out by using ANSYS finite element software and the method of combining explicit finite element method with artificial transmission boundary(MTF)The influence of predominant frequency,weak soil layer,layered structure and edge dip angle on time-frequency amplification characteristics of surface ground motion in the basin.The main contents of this paper are as follows:1.The calculation method of obliquely incident free field and the numerical simulation method of obliquely incident basin effect analysis using free field data are introduced.2.The effects of incident angle,wave type and preeminent frequency of incident wave on ground motion response of basin are studied respectively.The results indicate that(1)the incident angle has a significant influence on the time-frequency domain ground motion of the basin surface.The peak displacement of the horizontal component in the edge area of the basin increases with the increase of incident angle,while the peak displacement in the middle and right area decreases;the peak displacement of the vertical component in all areas of the basin increases with the increase of incident angle.The magnification factor of horizontal component increases with increasing incident angle and the vertical component decreases with increasing incident angle.The Fourier spectrum ratio of observation points increases with the increase of incident angle;(2)Under different types of seismic wave input,the seismic magnification of the basin differs significantly.(3)Compared with pulse wave input,the magnification law of ground motion in the basin under actual seismic record input is more complicated.(4)The preeminent frequency of incident seismic wave has a significant influence on the time-frequency domain ground motion response of the basin surface.When the preeminent frequency of seismic wave is close to the natural frequency of the basin,resonance will occur and the ground motion response of the basin is strong.3.The effects of soft soil layer,layered structure of basin soil layer and dip angle of basin edge on the ground motion of basin are studied.The results show that:(1)when the soft soil layer is located on the surface of the basin,the soft surface soil has a significant amplification effect on the peak ground motion;when the soft soil layer is located in the middle of the basin,the high-frequency component ground motion is significantly suppressed,while the low-frequency component ground motion is significantly amplified.(2)The maximum displacement of horizontal component increases with the increase of the number of soil layers.(3)The smaller the dip angle,the more obvious the focusing effect of seismic wave.