2003 Fiscal Year Final Research Report Summary
OBSERVATIONAL RESEARCH ON CRUSTAL STRUCTURE AROUND M6.1 EARTHQUAKE FAULT
| Project/Area Number |
13440128
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 |
NISHIMURA Takeshi TOHOKU UNIVERSITY, GRADUATE SCHOOL OF SCIENCE, ASSOCIATE PROFESSOR, 大学院・理学研究科, 助教授 (40222187)
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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)
TANAKA Satoru TOHOKU UNIVERSITY, GRADUATE SCHOOL OF SCIENCE, RESEARCH ASSOCIATE, 大学院・理学研究科, 助手 (60281961)
SATO Haruo TOHOKU UNIVERSITY, GRADUATE SCHOOL OF SCIENCE, PROFESSOR, 大学院・理学研究科, 教授 (80225987)
NAKAMURA Ayako TOHOKU UNIVERSITY, GRADUATE SCHOOL OF SCIENCE, RESEARCH ASSOCIATE, 大学院・理学研究科, 助手 (70312543)
YAMAMOTO Hidekazu IWATE UNIVERSITY, FACULTY OF ENGINEERING, ASSOCIATE PROFESSOR, 工学部, 助教授 (00250639)
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| Project Period (FY) |
2001 – 2003
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| Keywords | Temporal change / Crustal structure / Iwate volcano / Earthquake / Artificial seismic source / Earthquake family |
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| Research Abstract |
We investigate temporal changes of crustal structure around the 1998 M6.1 earthquake occurred south west of Volcano Iwate by analyzing seismic signals excited by artificial seismic experiments from 1998 to 2003 and by analyzing seismic waves of earthquake families occurring on the Pacific plate boundary. The seismic signals excited by the active shots were recorded by short period and broad band seismometers installed at permanent stations (GNB, ANS, AKM) of Tohoku University and a temporal station (MTI). We estimate phase difference of nearby two seismograms for the six shots by using a cross spectrum method. Then, we evaluate the seismic velocity changes of the structure during the two shots. The results show that the seismic velocity decreases about 1.5% at MTI and GNB stations, which are located at the northern edges of the fault, for shot 1 and shot 2, during which the M6.1 earthquake occurred. Then, the seismic velocity increases of about 0-0.5% is observed for the data from 1998 (after the M6.1 eq.) to 2002. From 2002 to 2003, about 0.3% velocity increase is observed again. Cross-correlation analyses of the earthquake families also show a significant temporal change of heterogeneity around the M6.1 earthquake and Volcano Iwate. We infer that these changes in shallow that are observed from 1998 to 2002 are related to stress release and accumulation of the M6.1 earthquakes and/or structure changes due to the intense volcanic activity of Mt Iwate at this period. We further determined a three-dimensional P-wave velocity structure around the M6.1 earthquake and the spatial distribution of slip and high-frequency wave radiation zone for the M6.1 earthquakes.
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