Study on scattering of seismic waves in the heterogeneous structure of the earth and their envelope formation

岩石圈是地球上从地表到深度约100公里的一个区域，它是一种非均匀的弹性介质。本文基于波动方程和辐射传递理论，提出了一种在随机非均匀介质中合成包络的方法。然后，我们将观测到的微地震的地震记录包络与地球介质速度波动谱的关系进行了分析。我们也注意到长周期表面波的包络。下面，我们对本研究的结果进行总结：1。利用马尔可夫近似建立了三维随机介质中球向外标量波的模拟方法。通过与有限差分法模拟的包络波的比较，验证了该方法的正确性。通过对日本东北地区微地震s波记录的包络分析，揭示了速度非均匀性的功率谱。利用球形地球上瑞利波能量的单散射模型，成功地解释了100-200s周期垂直分量地震记录的包络线。此外，基于辐射传递理论，我们成功地推导了表面波的多次散射过程。通过对1998年岩手山地震人工爆炸资料的交叉谱分析，发现了地震前后地震波传播速度和散射特性的变化。利用扩展尾波归一化方法定量测量了韩国东南部地壳的纵、横波衰减。从室内实验中，我们发现超声波的包络在很大程度上依赖于岩石样品的非均质谱。首席研究员写了两篇关于地震波散射的综述，一篇关于尾波的综述，一篇关于包络层形成的综述。

The lithosphere, a region of the Earth from the ground surface to a depth of about 100 km, is heterogeneous as an elastic medium. In this study, we develop a method, to synthesize envelopes in randomly inhomogeneous media based on the wave equation and the radiative transfer theory. Then, we analyze seismogram envelopes of micro earthquakes observed in relation with the spectra of yelocity fluctuations of the earth medium. We also pay attention to envelppes of long period surface waves. In the following, we summarize the results of this research :1. We formulated the simulation method for spherically outgoing scalar waves in 3-D random media by using the Markov approximation. This method is justified from the comparison with wave envelopes simulated by using the finite difference method. The power spectra of velocity inhomogeneity were revealed from the envelope analysis of S-wave seismograms of micro earthquakes in Tohoku, Japan.2. We successfully explained the envelope of vertical-component seismograms at periods of 100-200s by using the single scattering model of Rayleigh wave's energy on the spherical earth. Furthermore, we have succeeded in formulating the multiple scattering process of surface waves based on the radiative transfer theory.3. We found a change in wave propagation velocity and scattering characteristics before and after the 1998 Mt. Iwate earthquake from the cross-spectra analysis of artificial explosion data. We quantitatively measured attenuation of P and S waves in the crust of southeastern Korea based on the extended coda normalization method. From the laboratory experiment, we found that envelopes of ultrasonic waves strongly depend on the heterogeneity spectra of rock samples.4. The head investigator wrote two review of seismic wave scattering, a review of coda, and a review of envelope formation.