Study On Seismic Effect Of Basin And Sub-Basin Based On Numerical Simulation

The Sub-basin in the Basin-and Sub basin can significantly enhance the duration and magnitude of ground motions,creating areas of anomalous intensity and causing more severe damage.In addition to the direct incident body wave at the bottom of the sub-basin,there are also laterally propagating surface waves generated by the large basin,which lead to changes in the resonance characteristics and amplification effect of the sub-basin.Therefore,the study of basin-sub-basin structure plays an important role in the prediction of complex basin intensity anomalies and the disaster prevention and seismic design in practical engineering.In this paper,the techniques of explicit finite element method combined with artificial boundary and spectral element method combined with parallel algorithm are used to simulate the ground motion response of basin-sub-basin models in two-dimensional and three-dimensional layers and analyze them in time and frequency domains.The main conclusions are as follows:1.Based on the explicit finite element method,the two-dimensional resonance frequencies and their corresponding amplification factors of the two-dimensional trapezoidal basin-sub-basin to the two-dimensional trapezoidal basin-sub-basin were compared and analyzed under the vertical incidence of SH and SV waves.Impact.The results show that:(1)Affected by the laterally propagating surface waves generated in the large basin,the maximum values of PGV and in the sub-basins are obviously amplified,and the amplification of SV waves is greater than that of SH waves.(2)The sub-basin impedance ratio has a great influence on the maximum values of PGV and,two-dimensional resonance frequency and its corresponding amplification factor,but the large basin dip angle and half-width have little effect.Compared with a single small basin,the two-dimensional resonance frequency of the sub-basin increases under the incidence of SV and SH waves,and the increase of the incidence of SV waves is greater than that of SH waves under the same impedance ratio.The amplification factor of the two-dimensional resonance frequency under the SH wave incidence is basically larger than that of a single small basin,while the SV wave is lower than the single small basin under the low impedance ratio,and higher than the single small basin and the SH wave incidence under the high impedance ratio.The two-dimensional resonance frequency of the basin-sub-basin under the incident SV wave and its corresponding amplification factor are more affected by the large basin than the SH wave.2.Based on the spectral element method to simulate the ground motion response of the three-dimensional single small basin model and the basin-sub-basin model with four dip angles under the action of point sources at three depths,the Fourier spectrum ratio of the basin model and the bedrock half-space model The resonance frequency and amplification characteristics of the 3D basin-sub-basin model are analyzed.The results show that:(1)The resonance frequency of the 3D basin-sub-basin model is 1.5times that of the 2D model.(2)The increase of the dip angle of the basin causes the resonance frequency of the sub-basin to decrease by about 5%,and also causes the amplification factor of the central area of the basin to increase by 1.3-1.8 times.(3)The increase of the focal depth will reduce the magnification factor of the sub-basin,from 2.3 to 1.3.(4)Affected by the incident direction of the source,when the source is shallow,the maximum magnification area in the sub-basin is concentrated in the southeast of the basin;when the source is deep,the maximum magnification area in the sub-basin is basically concentrated in the center of the basin.(5)The magnification ratio(BSB/SB)of the basin-sub-basin to a single small basin reaches the maximum value at the edge of the sub-basin,and basically has a maximum value at the edge of the back wave surface of the basin when the source increases.3.Based on the spectral element method to simulate the response of the threedimensional ellipsoid basin-sub-basin model under four sets of stochastic finite fault models,the relationship between the depth of the basin,the period of the response spectrum and the amplification factor was studied through the response spectrum ratio between the basin model and the bedrock half-space model.The results show that:(1)The PGA of the north-south component in the sub-basin is larger than the east-west and vertical directions,and is basically not affected by the fault.(2)The basin model achieves the maximum amplification factor at the maximum depth and the longest period,which is about 3.2.(3)The magnification under the long period(8s)in the range of 1-2km is dominant,while the difference between the magnification under different periods at the shallow basin and the deep basin is not large.