S-wave attenuation structure on the western side of the Nankai subduction zone: implications for fluid distribution and dynamics
S-wave attenuation structure on the western side of the Nankai subduction zone: implications for fluid distribution and dynamics
复制标题
南开俯冲带西侧横波衰减结构：对流体分布和动力学的影响
DOI：
10.1002/2014jb011103
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Yoshiyuki Kaneda
中科院分区：
文献类型：
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作者：
Tsutomu Takahashi;Koichiro Obana;Yojiro Yamamoto;Ayako Nakanishi;Shuichi Kodaira;Yoshiyuki Kaneda
我们通过分析4-8、8-16和16-32 Hz的最大S波振幅以及多次前向散射引起的视振幅衰减的校正项，估计了日本西南部和南海海槽西部的S波衰减结构。由于广角散射，我们在层析成像研究中估计的衰减（Q−1）远大于Q − 1，因此我们估计的Q − 1主要由固有衰减组成。高衰减区域（4-8 Hz时Q−1> 1/300）在第四纪火山下方和四国以南海域成像。低Q（4-8 Hz时<1/1500）或中等Q −1（4-8 Hz时为1/500-1/1000）的图像出现在四国和中国的非火山地区。四国岛及周边地区的高Q − 1和中Q − 1位于俯冲菲律宾海板块的顶部附近。这种对应关系意味着这些高Q − 1和中等Q − 1反映了俯冲板片中的流体。通过应用水饱和多孔随机介质中衰减的理论模型，我们研究了低频（<1 Hz）地震波引起的波致流体流动，这可能与表面波触发非火山震颤有关。尽管本研究中的Q − 1结构不能完全解释波致流体流动引发的震颤，但震颤区Q − 1的大不确定性表明，Q − 1和随机不均匀性的高分辨率成像将对渗透率和其他介质性质的空间变化产生一些限制。
We estimated theSwave attenuation structure in southwestern Japan and the western Nankai Trough by analyzing maximumSwave amplitudes at 4–8, 8–16, and 16–32 Hz with a correction term for apparent amplitude attenuation due to multiple forward scattering. Because the estimated attenuation (Q−1) in our tomographic study was much larger thanQ−1due to wide‐angle scattering, our estimatedQ−1was composed mainly of intrinsic attenuation. High‐attenuation areas (Q−1> 1/300 at 4–8 Hz) were imaged beneath Quaternary volcanoes and south off Shikoku. Low (<1/1500 at 4–8 Hz) or moderateQ−1(1/500–1/1000 at 4–8 Hz) was imaged beneath Shikoku and nonvolcanic areas of Chugoku. High and moderateQ−1in and around Shikoku are located near the top of subducting Philippine Sea Plate. This correspondence implies that these high and moderateQ−1reflect fluid in the subducting slab. By applying a theoretical model of attenuation in water‐saturated porous random media, we examined wave‐induced fluid flow induced by lower frequency (<1 Hz) seismic waves that may be related with triggering of nonvolcanic tremor by surface waves. Even thoughQ−1structure in this study cannot fully explain the tremor triggering by wave‐induced fluid flow, large uncertainties ofQ−1in tremor zone suggest that high resolution imaging ofQ−1and random inhomogeneities would give some constraints for the spatial variation of permeability and other medium properties.