Stress‐ and Structure‐Induced Shear‐Wave Anisotropy along the 1999 Izmit Rupture, Northwest Turkey
Stress‐ and Structure‐Induced Shear‐Wave Anisotropy along the 1999 Izmit Rupture, Northwest Turkey
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DOI：
10.1785/0120110270
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发表时间：
2012-10
影响因子：
3
通讯作者：
O. Hurd;M. Bohnhoff
中科院分区：
文献类型：
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作者：
O. Hurd;M. Bohnhoff
摘要我们利用1999年伊兹米特7. 4级地震后余震的地震图进行了横波分裂分析，以描述北安纳托利亚断层带（NAFZ）西北部下地壳中应力和结构控制的各向异性机制。使用互相关技术对直接剪切波到达进行分裂分析，以计算快剪切波极化和快剪切波与慢剪切波到达之间的延迟时间。位于NAFZ内（1公里）的五个台站产生了333个高质量的剪切波分裂测量值。剪切波分裂测量表明，偶尔可以在两种各向异性机制之间进行划分。距离NAFZ大于1 km的台站往往具有与最大水平压应力的区域走向平行或亚平行的主导快剪切波极化，这表明存在应力控制的各向异性机制。NAFZ 1 km范围内的单站产生了一个双峰主导快剪切波偏振，该偏振平行于和垂直于附近Mudurnu断层的走向。我们将断层平行模式解释为代表Mudurnu断层的结构控制各向异性机制。所有地震的平均延迟时间为0.038±0.031 s，各向异性间隔似乎不超过8 km。快速剪切波偏振和延迟时间表明记录阵列内存在非均匀各向异性分布，并且上地壳的物理性质在NAFZ和周围地区之间存在差异。
Abstract We perform a shear‐wave splitting analysis using seismograms of aftershocks following the 1999 M w 7.4 Izmit earthquake to delineate between stress‐ and structure‐controlled anisotropic mechanisms in the upper crust beneath the northwest North Anatolian fault zone (NAFZ). The splitting analysis is performed on direct shear‐wave arrivals using a cross‐correlation technique to calculate the fast shear‐wave polarization and the delay time between fast and slow shear‐wave arrivals. Five stations located both within ( 1 km) the NAFZ yield a combined 333 quality shear‐wave splitting measurements. The shear‐wave splitting measurements indicate that it is occasionally possible to delineate between the two anisotropic mechanisms. Stations greater than 1 km from the NAFZ tend to have dominant fast shear‐wave polarizations parallel or subparallel to the regional strike of the maximum horizontal compressive stress, which suggests a stress‐controlled anisotropic mechanism. The single station within 1 km of the NAFZ yields a bimodal dominant fast shear‐wave polarization that is both parallel and perpendicular to the strike of the nearby Mudurnu fault. We interpret the fault‐parallel mode as representing a structure‐controlled anisotropic mechanism from the Mudurnu fault. The average delay time for all earthquakes is 0.038±0.031 s, and anisotropic intervals do not appear to extend below 8 km. The fast shear‐wave polarizations and delay times suggest a heterogeneous anisotropic distribution within the recording array and that the physical properties of the upper crust vary between the NAFZ and surrounding area.