Study On The Site Effect Of Ground Motion In Baodi Area

Baodi area is located in the north of Tianjin,close to Beijing and Tangshan city.With the integration of Beijing,Tianjin and Hebei and the relaxation of Beijing's non capital functions,the location advantage of Baodi area is increasingly obvious,the urban scale is gradually expanding,and the traffic is increasingly convenient.In the face of the growth of urban population,the risk warning of earthquake and the influence of potential source on Baodi area are particularly important.In order to be able to deal with the adverse impact of future earthquakes on Baodi District in advance,this paper relies on major scientific and technological projects in Tianjin to study the influence of overburden,Baodi fault and Quaternary sedimentary environment on the ground motion effect in Baodi district.The experience and research of earthquake damage at home and abroad show that the site effect is an important factor that causes the local variation of earthquake disaster and ground motion,and it is mainly affected by the site velocity model.At the same time,the numerical simulation method can simulate the seismic wave propagation process in the three-dimensional stratum medium with complex structure,and obtain the ground motion response of the surface,and the accuracy of the numerical simulation depends on the accuracy of the underground velocity model.In this paper,through the analysis of the velocity structure of the existing borehole sediment layer,the relationship between the velocity structure and the depth of the sediment layer is established,and the wave velocity of the sedimentary layer is estimated by using the obvious characteristics of the sedimentary layer in the borehole,so that part of the borehole without wave velocity measurement is used for the construction of the site model,and then a three-dimensional velocity structure model of Baodi area that meets the requirements is established.At the same time based on the typical characteristics of the deposited layer divided Quaternary Quaternary geotechnical partition Baodi further study the effects of different sedimentary environments seismic response.Based on specfem3 d software of Linux system,the spectral element method is used to simulate the effect of moment tensor point source on three-dimensional ground motion.The main research contents and results are as follows:(1)The cloud maps of PGA,PGV and PGD distribution of free field and cover soil are similar,which are negatively correlated with epicenter distance.(2)The cover soil has obvious amplification effect on the ground motion of the site,and is affected by the Quaternary sedimentary environment and epicenter distance.Secondly,the existence of the site covering layer makes the ground motion waveform of each measuring point more complex and extends the duration of the ground motion response waveform.(3)The seismic response of Baodi fault to the site shows obvious up and down wall effect.At a point equidistant from the fault rupture trace,the peak value of the ground motion response at the upper wall is significantly greater than that of the lower wall,and the attenuation rate is also faster than the lower wall.(4)Through the deepsoil program,it is verified that the spectral element method has good applicability to simulate the ground motion response of complex geological environment,and can accurately obtain the ground motion response of each measuring point,which is of great significance for the earthquake disaster prevention of Baodi area.