A Volcanic Front as a Boundary of Seismic-Attenuation Structures in Northeastern Honshu, Japan
A Volcanic Front as a Boundary of Seismic-Attenuation Structures in Northeastern Honshu, Japan
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DOI：
10.1785/0120050085
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发表时间：
2006-04
影响因子：
3
通讯作者：
K. Yoshimoto;U. Wegler;M. Korn
中科院分区：
文献类型：
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作者：
K. Yoshimoto;U. Wegler;M. Korn
我们调查了日本本州东北部的 S 尾波能量的空间分布，那里的火山锋从北向南延伸。本研究对 Hi-net 记录的当地 6.4 级地震记录进行了分析。计算了 82 个地震台的尾波均方振幅，频率为 2-4、4-8、8-16 和 16-32 Hz。根据这些测量结果，在火山前缘从东（弧前）到西（弧后）观察到尾波能量的明显空间变化。尾波能量在弧前均匀分布，而在弧后发现随着水平偏移火山前缘呈指数下降。衰减率随着频率的增加而增加。我们提出了一个扩散吸收模型，以物理方式洞察观察到的尾波能量的区域变化。该模型成功地解释了观测到的特征，并预测弧后尾波能量的指数变化是扩散率和吸收系数的函数。通过假设散射系数值为 0.01 km -1，在 10 Hz 频率下，弧后固有衰减因子的大小估计约为 Q i -1 = 0.02。这种内在衰减因子大约是之前弧前研究报告的两倍。
We investigated the spatial distribution of S -coda-wave energy in northeastern Honshu, Japan, where a volcanic front runs from north to south. Seismograms of a local event with a magnitude of 6.4 recorded by the Hi-net were analyzed in this study. The mean square amplitudes of coda waves at 82 seismic stations were calculated for bands with frequencies of 2–4, 4–8, 8–16, and 16–32 Hz. From these measurements, a clear spatial variation of coda-wave energy was observed across the volcanic front from east (forearc) to west (backarc). The coda-wave energy is uniformly distributed in the forearc, whereas an exponential decrease with horizontal offset from the volcanic front is found in the backarc. The decay rate increases with increasing frequency. We propose a diffusion–absorption model to give a physical insight into the observed regional variation in coda-wave energy. This model explains the observed characteristics successfully and predicts that the exponential variation of coda-wave energy in the backarc is a function of the diffusivity and the absorption coefficient. The magnitude of the intrinsic attenuation factor in the backarc is estimated at about Q i −1 = 0.02 at a frequency of 10 Hz by assuming a value of 0.01 km −1 for the scattering coefficient. This intrinsic attenuation factor is about twice as large as those reported from previous studies on the forearc.