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大约100公里深处的一个区域，它是一种非均匀的弹性介质。在这项研究中，我们发展了一种方法，在随机非均匀介质的波动方程和辐射传输理论的基础上合成信封。然后，我们分析了所观测到的微地震的地震图包络与地球介质的黄度起伏谱的关系。我们还注意到长周期表面波的包络。本文主要研究内容如下：1.利用马尔可夫近似，给出了三维随机介质中球形出射标量波的模拟方法。通过与有限差分法模拟的波包的比较，验证了该方法的正确性。通过对日本东北地区小震S波记录的包络分析，揭示了速度不均匀性的功率谱。利用瑞利波能量在球形地球上的单次散射模型，成功地解释了周期为100- 200秒的垂直分量地震记录的包络。此外，我们还成功地建立了基于辐射传输理论的表面波多次散射过程.我们发现，在1998年山前后的波传播速度和散射特性的变化。从人工爆破数据对岩手地震的互谱分析。我们定量测量的P波和S波的衰减在韩国东南部的地壳扩展尾波归一化方法的基础上。通过室内实验，我们发现超声波的包络线强烈地依赖于岩石样品的非均匀性谱.首席研究员撰写了两篇地震波散射综述、一篇尾波综述和一篇包络形成综述。

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.