Changes in the stress field after the 2008 M7.2 Iwate‐Miyagi Nairiku earthquake in northeastern Japan
Changes in the stress field after the 2008 M7.2 Iwate‐Miyagi Nairiku earthquake in northeastern Japan
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DOI：
10.1002/2014jb011291
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发表时间：
2014-12
期刊：
影响因子：
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通讯作者：
Keisuke Yoshida;A. Hasegawa;T. Okada;T. Iinuma
中科院分区：
文献类型：
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作者：
Keisuke Yoshida;A. Hasegawa;T. Okada;T. Iinuma
为了研究2008年日本东北部岩手宫城内陆7.2级地震后的应力场变化，我们利用主震后部署的密集余震观测网络和周边地区临时和常规观测站的数据，确定了震源区内的许多震源机制。应用应力张量反演这些震源机制数据，我们估计了详细的空间分布的主应力方向在这个事件的源区。最大主应力（σ1）轴的方向在主震前后有显著差异。在主震之前，σ1轴在整个研究区域内的方向为WNW‐ESE，与板块会聚方向平行。主震后，σ1轴的方向发生了明显的变化，并表现出明显的空间变异。余震区北方和南部距主震大滑移区较远，σ1轴向为WNW‐ESE，与主震前相似。相反，在余震区中部的东部和西部，σ1轴方向分别为N-S和NE-SW。这种σ1轴向的空间分布特征与主震破裂时的静态应力变化特征基本一致，表明主震破裂后的应力空间不均匀性是由这种静态应力变化引起的。主震前的差应力值小于10-30 MPa，表明主震断层较弱。
In order to investigate changes in the stress field following the 2008 M7.2 Iwate‐Miyagi Nairiku earthquake in NE Japan, we determined many focal mechanisms within the focal area, using data from both the dense aftershock observation network deployed just after the main shock and other temporary and routinely operated stations in the surrounding area. Applying stress tensor inversions to these focal mechanism data, we estimated the detailed spatial distribution of the principal stress orientations in this event's source area. Estimated orientations of the maximum principal stress (σ1) axes differ significantly before and after the main shock. Before the main shock, the σ1 axis is oriented WNW‐ESE across the entire studied area, which is parallel to the plate convergence direction. After the main shock, however, the orientation of the σ1 axis changed significantly and showed remarkable spatial variation. In the northern and southern parts of the aftershock area, located relatively far from the main shock large slip area, the σ1 axes are oriented WNW‐ESE, similar to those before the main shock. In contrast, to the east and west of the central part of the aftershock area, the σ1 axes are oriented N‐S and NE‐SW, respectively. This characteristic spatial pattern of σ1 axis orientations is approximately consistent with that of static stress change associated with the main shock rupture, which strongly suggests that the spatially heterogeneous stress after the main shock is caused by such static stress change. The differential stress magnitude before the main shock is estimated to be less than 10–30 MPa, suggesting that the main shock faults are weak.