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神户地震造成严重破坏的地区呈狭窄的带状分布是1995年兵库县南部(神户)地震非常显著的特征。形成强地面运动放大的过程至今未见阐述。通过构造一个掩埋于靠近盆地的走滑断层的一个M=7地震的动力学破裂过程,我们模拟了由破裂方向性产生的盆地边缘效应。通过三维有限差分方法计算了频率达1Hz的速度的地面运动地震图。峰值地面速度曲线的状态显示,当断层与盆地边缘平行对,峰值地面运动在沿盆地边缘一个宽度在几公里范围的狭窄带内被放大了。这一放大作用还与断层位置密切相关。然而,当整个断层同时破裂时,大振幅并没有集中于一个狭窄的地带内。这说明只有当破裂以有限的速度平行于盆地边缘传播时,在狭笮带内强烈地面振动才会发生。这种情况看来就是神户地区所表现出来的,这一地区由破裂方向性导致的盆地边缘效应也许就是“严重破坏带”产生的原因。
The narrow band-shaped distribution in the area severely damaged by the Kobe earthquake was a very significant feature of the southern Hyogo earthquake in 1995. The process of forming a strong ground motion amplification has not been elaborated. By modeling the dynamic rupture of an M = 7 earthquake buried in a strike-slip fault near the basin, we simulated the basin edge effect caused by the fracture directionality. The ground motion seismograms with frequencies up to 1 Hz were calculated by three-dimensional finite difference method. The state of the peak ground velocity curve shows that when the fault is parallel to the edge of the basin, the peak ground motion is magnified within a narrow band of several kilometers along the edge of the basin. This magnification is also closely related to the location of the fault. However, when the entire fault ruptured at the same time, the large amplitude was not concentrated in a narrow zone. This shows that strong ground vibrations within the stilt zone only occur when fractures propagate parallel to the basin margin at a limited rate. This seems to be the case in the Kobe area, where the marginal effect of the basin, caused by the directionality of the rupture, may have contributed to the “serious damage zone.”