Two Dimensional Basin Amplification Statistical Analysis Based On Spectral Element Method

Based on the spectral element method,this paper adopts four basin models with different dip angles,and simulates 192 working conditions by changing the medium parameters and dimensionless frequencies inside and outside the basin,the amplification rule of two-dimensional basin with different focal depth,strike slip seismic and non plane wave incidence is studied.By comparing the velocity time histories of surface observation points under different basin dip angles and different focal depths,the peak value of velocity peak ratio and the position of the maximum value of velocity peak ratio are analyzed,and the relationship between the peak value and position of basin edge amplification and dimensionless frequency,focal depth and basin dip angle is analyzed.The results show that:1.Basin dip is an important parameter that affects the amplification effect of two-dimensional basins.With the increase of dimensionless frequency,the peak velocity ratio first increases and then decreases.There is little difference in the maximum velocity peak ratio of the four dip basins at low frequency.When the dimensionless frequency is greater than 1 and the dip angle is 15 °,the velocity peak ratio of the basin model changes greatly,which is in sharp contrast with that of other dip basin models,The position of the maximum velocity peak ratio in the basin with15 ° dip angle,whether horizontal or vertical,is very different from that in the basin with the other three dip angles.This may be due to the fact that the 15 ° basin has a longer slope than the basin at other angles.At the same dimensionless frequency,with the increase of basin dip angle,the position of the maximum velocity peak ratio is closer and closer to the left side of the basin.2.The change of focal depth will significantly affect the intensity of ground motion response.With the increase of focal depth,the maximum value of velocity peak to peak ratio in the horizontal direction gradually increases,reaches the maximum when the focal depth is 10 km,and then decreases.When the focal depth is shallow,there is little difference in the maximum value of velocity peak ratio in the horizontal direction of the four dip basins,and the difference is always less than 1;When the focal depth is deep and the frequency is high(η ≥ 1),the peak velocity ratio of the four dip basins varies greatly,and the maximum difference of the peak velocity ratio reaches 3.In the vertical direction,when the focal depth is shallow,the position of the maximum velocity peak ratio tends to the edge of the basin with the increase of the dip angle of the basin.In the horizontal direction,when the focal depth is shallow and the frequency is high,the position of the maximum velocity peak ratio tends to the edge of the basin with the increase of the dip angle of the basin.3.The impedance ratio has an obvious influence on the distribution characteristics of the significantly amplificated area of the basin.When the impedance ratio is small,there are many significant amplification areas in the basin;When the impedance ratio is large,the amplification area decreases and is limited to both sides of the basin.The impedance ratio increases and the velocity peak ratio increases.The location of the maximum velocity peak ratio will not appear in the center of the basin,and the impedance ratio does not affect the location of the maximum velocity peak ratio.