A shallow fault-zone structure illuminated by trapped waves in the Karadere–Duzce branch of the North Anatolian Fault, western Turkey
A shallow fault-zone structure illuminated by trapped waves in the Karadere–Duzce branch of the North Anatolian Fault, western Turkey
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土耳其西部北安纳托利亚断层卡拉德雷-迪兹杰分支的浅断层带结构被困波照亮
DOI：
10.1046/j.1365-246x.2003.01870.x
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发表时间：
2003
影响因子：
2.8
通讯作者：
M. Aktar
中科院分区：
文献类型：
--
作者：
Y. Ben‐Zion;Zhigang Peng;D. Okaya;L. Seeber;J. Armbruster;Naşi̇de Özer;A. Michael;Ş. Barış;M. Aktar
本文通过对1999年伊兹米特（Izmit）地震后6个月的大规模地震数据分析，讨论了北安那托利亚断层Karadere - Duzce分支的地下结构。在靠近断裂带的台站观测到的地震记录显示，P波和s波列车的运动放大和长周期振荡在附近的非断层台站不存在。对数千种波形的检查表明，这些特征通常是由远在断裂带之外的事件产生的。由不一定发生在断层中的事件产生的断裂带地震记录中的异常特征一般可称为与断裂带有关的现场效应。在这些地震记录中，直S到达后的振荡横波列被分析为在低速断裂带层中传播的圈闭波。S波到达和困波群之间的时间差并不随着震源-接收距离沿断层的增加而系统地增长。这些观测结果表明，Karadere - Duzce断裂带的地震能量捕获是由浅层断裂带层产生的。行时分析和合成波形建模表明，捕获结构的深度约为3 ~ 4 km。合成波形模型进一步表明，浅层圈闭结构具有有效的波导特性，包括厚度约为100 m，相对于围岩的速度减少约50%，s波质量因子为10‐15。该结果得到了大型二维和三维参数空间研究的支持，并且与最近对许多其他断层和破裂带的困波的分析相一致。推断出的浅圈闭构造可能是断裂带的共同构造元素，可能对应于花型构造的顶部。与断裂带相关的场地效应相关的运动放大增加了断裂带构造附近的地震震动危险性。这种效应可能是显著的，因为在浅层圈闭结构中能够产生运动放大的震源体积很大。
SUMMARY We discuss the subsurface structure of the Karadere‐Duzce branch of the North Anatolian Fault based on analysis of a large seismic data set recorded by a local PASSCAL network in the 6 months following the Mw = 7.4 1999 Izmit earthquake. Seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long-period oscillations in both P- and S-wave trains that do not exist in nearby off-fault stations. Examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone. The anomalous features in fault-zone seismograms produced by events not necessarily in the fault may be referred to generally as fault-zone-related site effects. The oscillatory shear wave trains after the direct S arrival in these seismograms are analysed as trapped waves propagating in a low-velocity fault-zone layer. The time difference between the S arrival and trapped waves group does not grow systematically with increasing source‐receiver separation along the fault. These observations imply that the trapping of seismic energy in the Karadere‐Duzce rupture zone is generated by a shallow fault-zone layer. Traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3‐4 km. The synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m, a velocity decrease relative to the surrounding rock of approximately 50 per cent and an S-wave quality factor of 10‐15. The results are supported by large 2-D and 3-D parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones. The inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower-type structure. The motion amplification associated with fault-zone-related site effects increases the seismic shaking hazard near fault-zone structures. The effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large.