Seismic attenuation structure associated with episodic tremor and slip zone beneath Shikoku and the Kii peninsula, southwestern Japan, in the Nankai subduction zone
Seismic attenuation structure associated with episodic tremor and slip zone beneath Shikoku and the Kii peninsula, southwestern Japan, in the Nankai subduction zone
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DOI：
10.1002/2015jb012493
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发表时间：
2016-03-01
影响因子：
3.9
通讯作者：
Matsubara, Makoto
中科院分区：
文献类型：
--
作者：
Kita, Saeko;Matsubara, Makoto
利用S尾波频谱比方法对来自密集永久地震台网的波形数据估计的t*，分析了日本西南部下方的三维地震衰减结构（与频率无关的Q）。四国、纪伊半岛和九州东部约50 km深度的地震衰减（Q（p）（-1））结构清晰可见。在5 ~ 35 km深度，四国和纪伊半岛西南部的中央构造线和其他地质边界处的地震衰减结构发生变化。高Q（p）区内的下地壳的覆盖板块被发现就在滑动区的长期慢滑事件（SSE）的中心下方的丰后和纪伊海峡和四国中部。在四国中部之下，在上覆板块内，从陆面到俯冲板块的板块界面，存在一个由低Q（p）区包围的高Q（p）区。高Q（p）区和低Q（p）区分别对应于前人研究的高Vp区和低Vp区。高Q（p）区和低Q（p）区的边界与地震的分段边界（短期SSE的分段边界）一致。这些结果表明，长期和短期的SSE的位置可以限制的材料和/或条件的不均匀分布的上覆板块，这是由于地质和地理过程中形成的。弧前地壳内部物质和条件的不均匀性可能会影响界面上流变强度的不均匀分布。
The three-dimensional seismic attenuation structure (frequency-independent Q) beneath southwestern Japan was analyzed using t* estimated by applying the S coda wave spectral ratio method to the waveform data from a dense permanent seismic network. The seismic attenuation (Q(p)(-1)) structure is clearly imaged for the region beneath Shikoku, the Kii peninsula, and eastern Kyushu at depths down to approximately 50km. At depths of 5 to 35km, the seismic attenuation structure changes at the Median tectonic line and other geological boundaries beneath Shikoku and the southwestern Kii peninsula. High-Q(p) zones within the lower crust of the overlying plate are found just above the slip regions at the centers of the long-term slow-slip events (SSEs) beneath the Bungo and Kii channels and central Shikoku. Beneath central Shikoku, within the overlying plate, a high-Q(p) zone bounded by low-Q(p) zones is located from the land surface to the plate interface of the subducting plate. The high-Q(p) zone and low-Q(p) zones correspond to high-V-p and low-V-p zones of previous study, respectively. The boundaries of the high- and low-Q(p) zones are consistent with the segment boundaries of tremors (segment boundaries of short-term SSEs). These results indicated that the locations of the long- and short-term SSEs could be limited by the inhomogeneous distribution of the materials and/or condition of the overlying plate, which is formed due to geological and geographical process. The heterogeneity of materials and/or condition within the fore-arc crust possibly makes an effect on inhomogeneous rheological strength distribution on the interface.