2001 Fiscal Year Final Research Report Summary
Study on scattering of seismic waves in the heterogeneous structure of the earth and their envelope formation
| Project/Area Number |
12640400
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体地球物理学
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| Research Institution | Tohoku University |
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Principal Investigator |
SATO Haruo Tohoku University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (80225987)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAHARA Hisashi Tohoku University, Graduate School of Science, Research Associate, 大学院・理学研究科, 助手 (20302078)
YOSHIMOTO Kazuo Tohoku University, Graduate School of Science, Research Associate, 大学院・理学研究科, 助手 (10281966)
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| Project Period (FY) |
2000 – 2001
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| Keywords | Lithosphere / Scattering / Heterogeneity / Shear waves / Rayleigh waves / Coda / Wave equation / Random media |
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| Research Abstract |
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.
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[Publications] Sato, H., M. Fehler, and R-S, Wu: "Scattering and attenuation of seismic waves in the lithosphere"Chapter 13 of International Handbook of Earthquake And Engineering Seismology (Eds. W. H. K. Lee, H.Kanamori, P. C. Jennings, and C. Kisslinger), Academic Press, New York , (in press.). (2002)
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