Influence of rupture velocity of the directly-beneath fault on the basin seismic effect
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摘要: 首先基于有限断层破裂下的运动学震源模型，对比验证了三维谱元法对于近场地震动的模拟精度。 进而通过含盆地模型与不含盆地的一维水平成层模型的地震动强度之间和放大系数分布特征之间的对比，详细研究了直下型断层的破裂速度对盆地地震效应的影响。结果表明，盆地的存在会显著改变近断层地震动的分布特征，同时盆地内不同分量强地震动的分布特征变化较大。断层破裂速度对盆地地震效应影响显著，随破裂速度的增大盆地地震动强度逐渐增加，但不同分量上地震动强度的增加速率显著不同，受盆地效应的影响，放大系数表现出与强地震动不同的分布特征。盆地放大系数整体表现出随破裂速度的增加而减小的趋势，但不同分量放大系数所受影响程度差异明显。同时，盆地内地震动强烈放大区域的位置也受破裂速度的显著影响，但其总体上集中在断层两侧区域及垂直于破裂方向的盆地边缘附近。Abstract: Earthquakes caused by strike-slip fault often lead to serious earthquake damage to the cities above the basin when the fault rupture parameters have a significant effect on basin amplification. In this paper, the simulation accuracy of 3D spectral element method for near field vibration is contrasted under the kinematic source model based on the finite fault rupture. Then, by comparing the distribution characteristics of seismic intensity and amplification factor between the basin model and the one-dimensional horizontal layered model with no basin, the influence of the rupture velocity of the fault buried directly beneath the basin on the seismic effect of the basin is studied in detail. The results show that the existence of the basin will significantly change the distribution characteristics of near-fault ground motions, but the distribution characteristics of strong ground motions of different components in the basin will be significantly different. The amplification factor appears different distribution characteristics from strong ground motion with the influence of basin effect. The influence of fault rupture velocity on seismic effect of basin is significant. With the increase of rupture velocity, the ground motion intensity of the basin increases gradually, but the increase rate of different components is significantly different. The amplification factor of the basin overall shows a trend of decreasing with the rupture velocity increasement, but the influence degree for the amplification factor of different components is obviously different. Meanwhile, the location of the area with strong amplification in the basin is also significantly affected by the rupture velocity, but generally concentrated on both sides of the fault as well as near the basin edge perpendicular to the rupture direction.
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图 2 震源钟形滑动速率时间函数的时程 （a）及其对应的傅里叶振幅谱 （b）
Figure 2. Source bell-shaped slip-rate time history （a） and its Fourier spectrum （b）
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图 3 谱元程序和COMPSYN程序模拟得到的观测点A沿x向的结果与全空间解析解对比
（a） 位移时程；（b） 位移时程对应的频谱
Figure 3. Comparison of the simulated results of point A along the x direction obtained from the spectral element method and COMPSYN program and full-space analytical solution
（a） Displacement time-history；（b） Corresponding spectrum
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图 5 模型观测点分布
（a） 整个模型的地表区域；（b） 局部放大的盆地地表区域
Figure 5. Distribution of observation points for the model
（a） The surface area of the whole model； （b） The surface area of the enlarged basin
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图 6 震源滑动速率时间函数（a）及其对应的傅里叶振幅谱（b）
Figure 6. Slip rate time function （a） and its Fourier spectrum （b） of the source
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图 7 FP分量的水平成层模型PGV （a）、含盆地模型PGV （b）、盆地内PGV （c）及盆地内PGV放大系数AF （d）的分布
Figure 7. Distribution of PGV of horizontal stratification model （a）， PGV of basin model （b），PGV inside the basin （c） and amplification factor of PGV inside the basin （d） of FP component
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图 8 FN分量的水平成层模型PGV （a）、含盆地模型PGV （b）、盆地内PGV （c）及盆地内PGV放大系数AF （d）的分布
Figure 8. Distribution of PGV of horizontal stratification model （a），PGV of basin model （b），PGV inside the basin （c） and amplification factor of PGV inside the basin （d） of FN component
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图 9 UD分量的水平成层模型PGV （a）、含盆地模型PGV （b）、盆地内PGV （c）及盆地内PGV放大系数AF （d） 的分布
Figure 9. Distribution of PGV of horizontal stratification model （a），PGV of basin model （b），PGV inside the basin （c） and amplification factor of PGV inside the basin （d） of UD component
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图 10 不同破裂速度vr下盆地内三分量的峰值速度PGV分布
（a） 平行断层走向分量；（b） 垂直断层走向分量；（c） 竖向分量
Figure 10. Distribution of PGV for three components in the basin under different rupture velocities vr
（a） Fault-strike-parallel component； （b） Fault-strike-perpendicular component； （c） Vertical component
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图 11 不同破裂速度vr下盆地内三分量的放大系数AF分布
（a） 平行断层走向分量；（b） 垂直断层走向分量；（c） 竖向分量
Figure 11. Amplification factor distribution of three components in the basin under different rupture velocities vr
（a） Fault-strike-parallel component； （b） Fault-strike-perpendicular component； （c） Vertical component
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图 12 不同破裂速度vr下盆地内三分量峰值速度PGV的最大值（a）及平均值（b）
Figure 12. Maximum （a） and average （b） value of PGV for three components in the basin under different rupture velocities vr
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图 13 不同破裂速度vr下盆地内三分量峰值速度PGV的放大系数AF的最大值（a）及平均值（b）
Figure 13. Maximum （a） and average （b） values of amplification factor for three components PGV in the basin under different rupture velocities vr
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图 14 破裂速度vr＝1.44 （a），1.68 （b），1.92 （c）和2.16 （d） km/s时观测点B模拟FN分量的速度时程频谱
Figure 14. Spectrum of velocity time-history for FN component of point B when rupture velocities vr＝1.44 （a），1.68 （b），1.92 （c） and 2.16 （d） km/s，respectively
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图 15 阻抗比IC分别为4.33 （a）和24.32 （b）时盆地内FN分量的PGV分布
Figure 15. PGV distribution of FN component in the basin when impedance contrast IC is 4.33 （a） and 24.32 （b）
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图 16 阻抗比IC分别为4.33 （a）和24.32 （b）时盆地内FN分量的放大系数AF分布
Figure 16. Amplification factor AF distribution of FN component in the basin when impedance contrast IC is 4.33 （a） and 24.32 （b）
表 1 盆地模型的介质参数
Table 1 Medium parameters of basin model
名称 vS/（km·s−1） vP/（km·s−1） ρ/（g·cm−3） 盆地外 2.4 5.2 2.4 盆地内 0.7 2.0 1.9 
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表 2 不同阻抗比模型的介质参数对比
Table 2 Comparison of medium parameters for different impedance contrast model
vS/（km·s−1） ρ/（g·cm−3） 阻抗比IC
（盆地外/盆地内）盆地外 盆地内 盆地外 盆地内 改变前 2.4 0.7 2.4 1.9 4.33 改变后 3.0 0.256 4.15 2.0 24.32
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