1998 Fiscal Year Final Research Report Summary
Study on estimation of fluctuation in stress field and its relationship on activity of fault
| Project/Area Number |
09640500
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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 |
OKADA Tomomi Tohoku University Graduate School of Science, Research Assistant, 大学院・理学研究科, 助手 (30281968)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUZAWA Toru Tohoku University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (20190449)
HORIUCHI Shigeki National Institute for Earth Science and Disaster Prevantion, Head of Division o, 科学技術庁・防災科学技術研究所, 部長 (00004490)
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| Project Period (FY) |
1997 – 1998
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| Keywords | inland earthquake / active fault / stress / fault plane solution / moment tensor inversion / aftershock |
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| Research Abstract |
First, we have developed a method which simultaneously determines focal mechanism solutions of many small earthquakes and source-region station corrections for short-period body wave amplitudes by inverting amplitude data of P, SV, SH waves together with P wave polarity data. In this inversion, we assumed that P and S waves attenuation factors along ray paths from hypocenters to each station can be expressed as a function of hypocentral distance, back azimuth and incident angle. We applied the present method to 170 aftershocks of the 1996 Onikobe earthquake (M5.9), which occurred in the central part of northeastern Japan. P-axes of almost all the obtained focal mechanism solutions are horizontal and oriented in the east-west direction, which are almost correspond to the regional stress field.
Second, we applied the body wave inversion to seismic waves observed with the short-period seismograph. We used observed waves include P and S waves which were corrected the character of seismometer. The validity of the short period body wave inversion was verified by comparing the moment tensor solution calculated by this study to the distribution of P-wave first motion. We applied the method to aftershocks of the earthquake occurred in the southwestern part of Fukushima prefecture, northeastern Japan, August 3, 1998 (M4.9). Almost of these solutions are same type like as the fault plane solution of main shock, but some, which occurred at the edge of aftershock area, are different type solutions.
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[Publications] Umino, N.T.Okada, A.Nakamura, J.Nakajima, T.Sato, S.Hori, T.Kono, K.Nida, S.Ueki, T.Matsuzawa, A.Hasegawa and H.Hamaguchi: "Aftershock distribution for the M6.1 earthquake of 3 September 1998 in Shizukuishi, Iwate prefecture, northeastern Japan" Katsudansou-Kenkyu. (in press.).
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