Imaging the seismic structure and stress field in the source region of the 2004 mid‐Niigata prefecture earthquake: Structural zones of weakness and seismogenic stress concentration by ductile flow
Imaging the seismic structure and stress field in the source region of the 2004 mid‐Niigata prefecture earthquake: Structural zones of weakness and seismogenic stress concentration by ductile flow
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DOI：
10.1029/2005jb004016
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发表时间：
2006-08
影响因子：
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通讯作者：
A. Kato;S. Sakai;N. Hirata;E. Kurashimo;T. Iidaka;T. Iwasaki;T. Kanazawa
中科院分区：
文献类型：
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作者：
A. Kato;S. Sakai;N. Hirata;E. Kurashimo;T. Iidaka;T. Iwasaki;T. Kanazawa
[1] 我们在 2004 年日本新泻县中部地震（逆冲断层）的震源区部署了密集的时态地震台网。通过使用双差断层扫描反演余震到达时间，阐明了详细的速度结构和准确的余震分布。为了研究应力场，还进行了使用第一运动数据的应力张量反演。主震断层上方上盘地震速度低于下盘，速度对比延伸至约10 km深度。沿主震破裂带的余震分布在低速体和高速体之间的尖锐边界周围。此外，与最大余震相关的余震似乎与下盘低速区和高速区之间的边界对齐。最大主应力(σ1)方向与GPS数据推断的区域压缩应变率轴一致，但在主震震源西南侧，σ1方位角逆时针旋转约20°。主震震源大致位于上盘结构横向变化和σ1方位角旋转的过渡区。地震速度和应力场的非均质结构，加上上地壳的延性变形，可能使震源区周围的发震应力集中，导致余震序列在构造边界上的复杂分布。
[1] We deployed a dense temporal seismic network in the source region of the 2004 mid-Niigata prefecture earthquake (thrust fault), Japan. A detailed velocity structure and accurate aftershock distributions were elucidated by inverting aftershock arrival times using double-difference tomography. A stress tensor inversion using the first-motion data was also conducted in order to investigate the stress field. The seismic velocities in the hanging wall above the main shock fault are lower than those in the footwall, with the velocity contrast extending to a depth of approximately 10 km. The aftershocks along the main shock rupture zone are distributed around the sharp boundary between the low- and high-velocity bodies. Furthermore, aftershocks associated with the largest aftershock appear to be aligned on a boundary between low- and high-velocity zones, in the footwall. The orientation of maximum principal stress (σ1) is consistent with the regional compressional strain rate axis inferred from GPS data, except in the southwestern side of the main shock hypocenter where the azimuth of σ1 rotates approximately 20° counterclockwise. The main shock hypocenter was located roughly at the transition zone where the structure of the hanging wall changes laterally and the azimuth of σ1 rotates. Heterogeneous structures of the seismic velocity and the stress field, combined with the ductile deformation of the upper crust, may have concentrated seismogenic stress around the hypocenter area to cause the complex distributions of aftershock sequence on structural boundaries.