Low-frequency tremors associated with reverse faults in a shallow accretionary prism
Low-frequency tremors associated with reverse faults in a shallow accretionary prism
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DOI：
10.1016/j.epsl.2009.08.005
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发表时间：
2009-09-30
影响因子：
5.3
通讯作者：
Kodaira, Shuichi
中科院分区：
文献类型：
--
作者：
Obana, Koichiro;Kodaira, Shuichi
在大板块间逆冲地震中，发震俯冲带的浅层部分被认为在海啸发生中起重要作用。在南开海槽发震带的上倾部分附近，展断层是增生棱镜中主要的逆活动断层，可能在1944年Kii半岛外Tonankai 8.2级地震等大型板块间地震中破裂。本文利用海底地震仪近距离观测了Kii半岛浅层增生棱镜中与逆断层相关的低频地震。地震的特点是主要频率范围为2-8赫兹，在10赫兹以上的频率范围内缺乏能量。它们的持续时间从几十秒到几分钟不等。它们的源头分布在南开海槽向陆坡上的三组。每个群集的活动持续了一天到两周。许多低频震动位于一个主要的展断层的最浅部分附近。低频震颤和先前报道的极低频地震的幕式活动表明，浅层增生三棱镜中存在逆断层，这表明增生三棱镜中的逆断层是有条件稳定的断层，在足够强的动力载荷下，例如由大地震引起的动力载荷，可能变得不稳定。这种反向断层，如典型的展断层，可以在大的板块间地震中破裂并产生大的海啸。(C) 2009 Elsevier B.V.版权所有
The shallow part of a seismogenic subduction zone is thought to play an important role in tsunami genesis during large interplate thrust earthquakes. Near the updip portion of the seismogenic zone along the Nankai trough, splay faults, which are major active reverse faults in the accretionary prism, likely rupture during large interplate earthquakes such as the 1944 M-w 8.2 Tonankai earthquake off Kii Peninsula. We observed low-frequency tremors associated with reverse faults in a shallow accretionary prism off Kii Peninsula at close range by using ocean bottom seismographs. The tremors were characterized by a dominant frequency range of 2-8 Hz and a lack of energy in the frequency range above 10 Hz. Their duration ranged from tens of seconds to a few minutes. Their source locations lay in three clusters on the landward slope of the Nankai trough. Activity in each cluster continued for from one day to two weeks. Many of the low-frequency tremors were located near the shallowest part of a major splay fault. The episodic activity of low-frequency tremors and of previously reported very-low-frequency earthquakes, which indicate reverse faulting in the shallow accretionary prism, suggests that the reverse faults in the accretionary prism are conditionally stable faults that can become unstable under sufficiently strong dynamic loading, such as that caused by a large earthquake. Such reverse faults, as typified by a splay fault, can rupture during large interplate earthquakes and generate large tsunamis. (C) 2009 Elsevier B.V. All rights reserved.