Study of the inhomogeneous structure of the earth from the analysis of scattering phenomena of broad band seismic waves

研究地球介质的非均匀结构对认识地球演化过程具有重要意义。我们进行了以下三项地震研究：基于高频地震波分析的岩石圈小尺度非均匀性：结合辐射传递理论和马尔可夫近似，构建了二维随机介质中整个标度波包络综合的混合模型。对二维弹性随机介质中矢量波传播的马尔可夫近似进行了推广，提出了一种新的综合模型，定量地解释了有限差分模拟合成的包络。随机非均匀性引起的散射很好地解释了所观察到的峰值振幅衰减和包络展宽。东北地区的包络展宽分析揭示了第四纪火山下的强散射。利用接收函数法对中国-四国地区莫霍和俯冲菲律宾海板块的深度剖面进行了较为严格的拟合。2.利用基于PREM的各向同性散射模型分析区域地震中ScS相周围的波包络，首先定量估计了4 ~ 10 s周期的地幔散射系数。长周期瑞利波的包络分析：我们分析了IRIS和F-net记录的长周期大地震的垂直分量地震图。阵列分析表明，在衰减时间早期，基模瑞利波占主导地位，但随着衰减时间的增加，由于下地幔衰减较小，高模态占主导地位。我们发现尾线衰减因子直接代表了下地幔的衰减因子。阐明了随机弹性半介质中瑞利波与体波的散射特性，为长周期包络综合奠定了坚实的基础。少

Study of inhomogeneous structure of the earth medium is important for understanding the evolution process of the earth. We performed three seismological studies as follows : 1.Small-scale inhomogeneity of the lithosphere based on the analysis of high-frequency seismic waves : Combining the radiative transfer theory and the Markov approximation, we constructed a hybrid model for the synthesis of the whole scalar-wave envelope in 2-D random media. Extending the Markov approximation for vector wave propagation in 2-D elastic random media, we proposed a new synthesis model, which quantitatively explains envelopes synthesized by the finite difference simulation. Scattering due to random inhomogeneity well explains the peak amplitude decay and the envelope broadening observed. Strong scattering beneath Quaternary volcanoes was revealed from the envelope broadening analysis in Tohoku district. We made the depth profile of the Moho and the subducting Philippine-sea plate in Chugoku-Shikoku dis … More trict by using the receiver function method. 2.Scattering characteristics in the mantle from the analysis of ScS phase in intermediate periods : Analyzing wave envelopes around the ScS phase of regional earthquakes by using the isotropic scattering model based on PREM, we first estimated quantitatively the scattering coefficient in the mantle for periods from 4 to 10 s. 3.Envelope analysis of long period Rayleigh waves : We analyzed vertical-component seismograms of large earthquakes in long periods recorded by IRIS and F-net. The array analysis revealed that the fundamental mode Rayleigh waves dominate early lapse times but higher modes dominate as lapse time increases because of small attenuation in the lower mantle. We find that the coda attenuation factor directly represents the attenuation factor in the lower mantle. Clarifying the scattering characteristics between Rayleigh waves and body waves in random elastic half media, we established the solid base for the envelope synthesis in long periods. Less