2006 Fiscal Year Final Research Report Summary
Study on medium heterogeneity beneath island arcs based on the analysis of seismic wave scattering
| Project/Area Number |
17540389
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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 |
Solid earth and planetary physics
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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) |
YAMAMOTO Mare Tohoku University, Graduate school of science, Assistant Professor, 大学院理学研究科, 助手 (30400229)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Seismic wave / solid earth / crust / mantle / heterogeneous structure / scattering / coda waves / island arc |
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| Research Abstract |
Source duration times of microearthquakes are short; however, apparent duration times of S wave envelopes increase with travel distance increasing caused by scattering due to medium inhomogeneities. We clarified that the medium inhomogeneity is stronger in the back-arc side of the volcanic front compared with that in the fore-arc side in Japan arc. In this research, extending this idea, we carefully measured the relation between the S-wave peak delay from the onset and the ray path. We also developed the envelope synthesis in random elastic media as the mathematical foundation for these analyses. We find that the peak delays are larger for ray paths traveling beneath Quaternary volcanoes than those for ray paths traveling between Quaternary volcanoes in northern Japan. That is, the medium inhomogeneity is stronger beneath Quaternary volcanoes, but the medium is homogeneous between them. Interpreting the partition of energy of teleseismic P and P coda waves into the transverse component as a measure of medium heterogeneity, we classified the lithospheric heterogeneity in the world : the medium heterogeneity is large at plate collision, zones and subduction zones; however, it is small in continents. On the basis of the Markov approximation we have developed the direct envelope synthesis of vector waves in random elastic media. We have successfully formulated the envelope syntheses for both the incidence of a plane wavelet and the radiation from a point source in 2-D and 3-D cases. Especially in 2-D, we have confirmed the validity by using the finite difference simulations.
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Research Products
(25 results)
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[Journal Article] Temporal changes in seismic velocity of the crust around Iwate volcano, Japan, as inferred from analyses of repeated active seismic experiment data from 1998 to 20032005
Author(s)
Nishimura, T., S.Tanaka, T.Yamawakil, H.Yamamoto, T.Sano, M.Sato, H.Nakahara, N.Uchidal., S.Hori, H.Sato
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Journal Title
Earth Planets Space 57
Pages: 491-505
Description
「研究成果報告書概要(和文)」より
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[Journal Article] Temporal changes in seismic velocity of the crust around Iwate volcano, Japan, as inferred from analyses of repeated active seismic experiment data from 1998 to 20032005
Author(s)
Nishimura, T., S.Tanaka, T.Yamawaki, H.Yamamoto, T.Sano, M.Sato, H.Nakahara, N.Uchida, S.Hori, H.Sato
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Journal Title
Earth Planets Space 57
Pages: 491-505
Description
「研究成果報告書概要(欧文)」より
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