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

地震波在地球非均质结构中的散射及其包络形成研究

基本信息

批准号：
12640400
负责人：
SATO Haruo
金额：
$ 2.18万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

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.

岩石圈是地球上从地面到深度约100公里的一个区域，作为一种弹性介质是不均匀的。在本研究中，我们基于波动方程和辐射传输理论，发展了一种合成随机非均匀介质中包络的方法。然后，我们分析了观测到的微震的地震记录包络与地球介质的黄速起伏频谱的关系。我们还注意到了长周期面波的发展。本文的主要研究成果如下：1.建立了基于马尔可夫近似的三维随机介质中球面出射标量波的数值模拟方法。通过与用有限差分方法模拟的波包进行比较，证明了该方法的正确性。通过对日本东北地区微震S波记录的包络分析，揭示了速度不均匀的功率谱。利用瑞雷波能量在球形地球上的单次散射模型，成功地解释了100-200s周期内垂直分量地震记录的包络。此外，基于辐射传输理论，我们成功地建立了面波的多次散射过程。我们发现在1998年地震前后，波的传播速度和散射特性发生了变化。岩手县地震来自人工爆炸数据的交叉谱分析。基于扩展尾波归一化方法，我们定量测量了朝鲜东南部地壳中P波和S波的衰减。从实验室实验中我们发现，超声波的包络强烈地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评论，一篇关于尾波的评论，以及一篇关于包络形成的评论。