Scattering of high-frequency P wavefield derived by dense Hi-net array observations in Japan and computer simulations for seismic wave propagations
Scattering of high-frequency P wavefield derived by dense Hi-net array observations in Japan and computer simulations for seismic wave propagations
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日本密集 Hi-net 阵列观测得出的高频 P 波场散射和地震波传播的计算机模拟
DOI：
10.1093/gji/ggs127
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
S. and T. Furumura
中科院分区：
文献类型：
--
作者：
Takemura;S. and T. Furumura
我们研究了高频地震波的散射特性，由于小尺度的速度波动分布在地壳和上地幔在日本的基础上的三分量短周期地震图的分析和比较有限差分法（FDM）模拟地震波传播使用各种随机随机速度波动模型。本文利用310个地壳浅源地震的高灵敏度密集台网波形资料，研究了地震波在非均匀结构中散射引起的横向分量P波能量分配（PEPT）随频率和震源距离的变化。当距离小于150 km时，PEPT随频率的增加而增加，在D = 50 ~ 150 km范围内，PEPT近似为常数。PEPT在D = 150 km以上突然增大，在高频（f> 4 Hz）较大。因此，在P波初至相的传播路径（上地壳、下地壳和莫霍面附近）周围，距离D = 150 km以上，可能会发生P波的强散射。我们还发现了PEPT值的区域差异，即PEPT值是大的弧后侧的日本东北部相比，日本西南部和弧前侧的日本东北部。这些来自浅源地震的PEPT结果表明，与其他地区相比，日本东北部弧后一侧的非均匀性浅层结构更强，更复杂。这些假设，即小尺度速度波动的深度和区域变化，检查3-D FDM模拟使用各种非均质结构模型。通过对比PEPT的观测特征和模拟结果发现，由于下地壳相对于上地壳具有更高的速度和更强的非均匀性，下地壳发生了强烈的地震波散射。为了解释观测到的区域差异，在日本东北部的弧后侧，需要具有3- 4%的更强波动和更小κ的速度波动模型。
We studied the scattering properties of high-frequency seismic waves due to the distribution of small-scale velocity fluctuations in the crust and upper mantle beneath Japan based on an analysis of three-component short-period seismograms and comparison with finite difference method (FDM) simulation of seismic wave propagation using various stochastic random velocity fluctuation models. Using a large number of dense High-Sensitivity Seismograph network waveform data of 310 shallow crustal earthquakes, we examined theP-wave energy partition of transverse component (PEPT), which is caused by scattering of the seismic wave in heterogeneous structure, as a function of frequency and hypocentral distances. At distance of less thanD= 150 km, the PEPTincreases with increasing frequency and is approximately constant in the range of fromD= 50 to 150 km. The PEPTwas found to increase suddenly at a distance of overD= 150 km and was larger in the high-frequency band (f> 4 Hz). Therefore, strong scattering ofPwave may occur around the propagation path (upper crust, lower crust and around Moho discontinuity) of theP-wave first arrival phase at distances of larger thanD= 150 km. We also found a regional difference in the PEPTvalue, whereby the PEPTvalue is large at the backarc side of northeastern Japan compared with southwestern Japan and the forearc side of northeastern Japan. These PEPTresults, which were derived from shallow earthquakes, indicate that the shallow structure of heterogeneity at the backarc side of northeastern Japan is stronger and more complex compared with other areas. These hypotheses, that is, the depth and regional change of small-scale velocity fluctuations, are examined by 3-D FDM simulation using various heterogeneous structure models. By comparing the observed feature of the PEPTwith simulation results, we found that strong seismic wave scattering occurs in the lower crust due to relatively higher velocity and stronger heterogeneities compared with that in the upper crust. To explain the observed regional difference, the velocity fluctuation model with 3–4 per cent stronger fluctuation and smallerκis required at the backarc side of northeastern Japan.