A normal-faulting seismic sequence triggered by the 2011 off the Pacific coast of Tohoku Earthquake: Wholesale stress regime changes in the upper plate
A normal-faulting seismic sequence triggered by the 2011 off the Pacific coast of Tohoku Earthquake: Wholesale stress regime changes in the upper plate
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DOI：
10.5047/eps.2011.06.014
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发表时间：
2011-09
期刊：
影响因子：
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通讯作者：
A. Kato;S. Sakai;K. Obara
中科院分区：
文献类型：
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作者：
A. Kato;S. Sakai;K. Obara
这里显示的是2011年日本东北部太平洋沿岸9.0级大地震后，在茨木县北方发生的正断层地震序列中，震源位置的重新定位。从北方茨木地区中心向北的震源深度剖面显示，在10 km以下的深度处，地震线向西倾斜40° ~ 50°。另一方面，从中心到南部的震源显示出一个交叉的几何形状，由共轭的向西倾和东倾平面在相同的深度。震源走向的倾角与正常大地震震源机制的节面大致一致，并表现出摩擦破坏准则的最佳取向。此外，2011年东北地震前后记录的震源机制的比较表明，应力场突然从水平挤压到伸展在研究区。应力剧烈变化的最合理的解释是，与上覆板块内伴随大的水平伸展变形的沟槽平行应力的减少相比，沟槽法向压应力的显著减少。
We here show relocated hypocenters within a seismic sequence with normal faults in the northern part of Ibaraki Prefecture, triggered after the M 9.0 2011 off the Pacific coast of Tohoku Earthquake. Depth-sections of the hypocenters from the center of the northern Ibaraki region to the north show an earthquake alignment dipping westwards at 40° to 50° at depths shallower than 10 km. On the other hand, hypocenters from the center to the south show a cross-cutting geometry consisting of conjugate westward- and eastward-dipping planes at the same depths. The dip angles of the hypocenter alignments are roughly consistent with the nodal planes of focal mechanisms of large normal earthquakes, and exhibit optimal-orientations in terms of the frictional failure criterion. Furthermore, comparison of the focal mechanisms recorded before and after the 2011 Tohoku Earthquake suggests that the stress field abruptly changed from horizontal compression to extension in the study area. The most plausible explanation of the drastic stress changes is a significant reduction in trench-normal compressive stress compared with reduction in trench-parallel stress accompanying large horizontal extensional deformation within the overlying plate.