考虑土体非线性及倾角影响的盆地地震响应研究

基于二维沉积盆地模型,采用D-P弹塑性模型模拟盆地的非线性特征。利用显式有限元与黏弹性边界结合的方法,通过改变盆地边缘倾角,在时域和频域内分析盆地地表的地震动响应,对比线性与非线性盆地地震反应的差异。结果表明:(1)土体非线性对整个盆地范围内地震动的影响都较显著。考虑非线性时地震动放大系数明显降低,降低幅度在30%~50%。同时,考虑非线性和倾角影响时最强烈放大区域的范围和位置变化,且很小倾角下的分布特征显著不同。(2)两分量的放大系数都有随边缘倾角的增大而增强的趋势,但均是盆地边缘区域受非线性的影响最为显著。此外,真实地震波输入下显著放大区域的范围及线性与非线性结果的差异程度相对更大。(3)考虑非线性时,对于不同频率地震波的放大系数差别明显,但都表现出从低频到高频谱比分布越来越复杂的现象,同时盆地倾角的影响程度随频率的增大更加明显。(4)考虑土体非线性并未改变地震波传播的总体特征,但各震相强度相对降低。

Seismic response of the basin considering the effect of soil nonlinearity and dip angle

Considering a 2D sedimentary basin model, the D-P elastoplastic model was used to simulate the nonlinear characteristics of the basin. Combining the explicit finite element method with the viscoelastic boundary method and changing the dip angle of the basin edge, the seismic response of the basin surface was analyzed in time and frequency domains, and the difference between linear and nonlinear seismic responses of the basin was compared. The following results are presented: (1) The influence of soil nonlinearity on ground motion in the entire basin is observed. Only considering the nonlinearity, the amplification factor of ground motion is reduced by 30%-50%. Meanwhile, considering the influence of nonlinearity and dip angle, as well as the range and position of areas with the strongest amplification change, the distribution characteristics under considerably small dip angles are different. (2) The amplification factors of the two components tend to increase with the edge dip angle, but the basin edge area is most affected by the nonlinearity. In addition, under the input of a real seismic wave, the range of significant amplification area and the difference between linear and nonlinear results are relatively large. (3) Considering the nonlinearity, the amplification factors of seismic waves with various frequencies are different. However, the distribution of the spectral ratio from low to high frequency is increasingly complex, and the influence of the basin dip angle becomes evident with the increase in frequency. (4) Considering the nonlinearity of soil, the overall characteristics of seismic wave propagation are maintained, but the strength of each seismic phase is reduced.