Fault Geometry at the Rupture Termination of the 1995 Hyogo-ken Nanbu Earthquake
Fault Geometry at the Rupture Termination of the 1995 Hyogo-ken Nanbu Earthquake
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DOI：
10.1785/0119990027
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发表时间：
2000-02
影响因子：
3
通讯作者：
H. Sekiguchi;K. Irikura;T. Iwata
中科院分区：
文献类型：
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作者：
H. Sekiguchi;K. Irikura;T. Iwata
利用波形反演方法研究了1995年兵库县南部地震破裂终止时的震源几何形状和滑动分布，假设破裂模型的东北部存在断层分支。从静态位移分布和科比以东（西宫地区）的破坏范围来看，冈本断层可能存在分支。为了排除在波形反演过程中受盆地边缘衍射波污染的数据，我们研究了其影响的时空变化，并与平面模型进行了比较，确定了适合数据的窗口。确定了三个子事件，在以前的作品中报道。最大的一次发生在淡路一侧的浅水区，而较小的两次发生在科比一侧的深水区（7公里）。我们在分支的深处发现了一个较小的子火山口。假设有分支时，总方差的减少量较大，ABIC值较小，表明了分支故障模型的优越性。分辨率检查表明，建议的分支部分上的滑动是物理性的，而不是由随机数据噪声或绿色函数中的系统误差引起的，这些误差是由对速度结构的错误估计引起的。通过对分叉断层附近两水准观测站间相对静态位移的计算，也表明分叉断层模型具有更大的实用性。滑动对分支断层的影响已经在使用3D有限差分法的近源地面运动模拟中显示出来（岩田等人，1999年）。在真实的三维速度结构中，通过对震源过程和波传播过程的模拟，较好地再现了损伤分布所指示的近震源区地震动特征分布。在科比东部（Nada和Higashi-Nada区）、芦屋和西宫市，分支断层上的滑动影响了地面运动，但即使在这些地区，其贡献也不占主导地位;在0.1至1.0 Hz的频率范围内，约有30%至50%的最大速度。认为冈本断层在兵库县南部地震中的分叉破裂是这次地震震源过程的较好解释。这支持了地质观测所提出的几何障碍的想法。
The source geometry and slip distribution at rupture termination of the 1995 Hyogo-ken Nanbu earthquake were investigated using waveform inversion on the assumption of fault branching in the northeastern part of the rupture model. Possible branching of the Okamoto fault is suggested both by the static-displacement distribution and damage extension east of Kobe (Nishinomiya area). To exclude data contaminated by the basin-edge-diffracted wave in the waveform-inversion process, we examined the spatio-temporal variation of its influence and from a comparison with a flat model, we determined windows appropriate for the data. Three subevents were identified, as was reported in previous works. The largest was in the shallow part on the Awaji side, whereas the smaller two occurred at great depths (7km) on the Kobe side. We found a smaller subevent in the deep part of the branch. Total variance reduction was larger, and the ABIC value was smaller when we assumed the branch than when we did not, which shows the superiority of the branching fault model. Resolution checks showed that the slips on proposed branched portions are physical and not caused by random-data noise or systematic errors in Green's func- tions that arise from misestimation of velocity structures. Calculation of the relative static displacement between two leveling observation stations near the branching fault also showed the greater utility of the branching fault model. The effect of slip on the branched fault has been shown in near-source ground-motion simulation using the 3D finite-difference method (Iwata et al., 1999). The characteristic distribution of ground motion in the near-source region indicated by the damage distribution is well reproduced by the modeling of both the source process and wave propagation in the realistic 3D velocity structure. Slip on the branched fault affected the ground motion in eastern Kobe (Nada and Higashi-Nada wards), Ashiya, and Nishinomiya cities, but its contribution is not dominant even in those regions; about 30 to 50% maximum velocity in the frequency range of 0.1 to 1.0 Hz. We conclude that branching rupture of the Okamoto fault during the Hyogo-ken Nanbu earthquake is the preferable interpretation on the source process of this earth- quake. This supports the idea of a geometrical barrier suggested by geological ob- servations.