1999 Fiscal Year Final Research Report Summary
Integrated monitoring system for stress changes in rock
| Project/Area Number |
10554020
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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 | 展開研究 |
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| Research Field |
固体地球物理学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
YANAGIDANI Takashi Kyoto Univ., DPRI, Associate Prof., 防災研究所, 助教授 (00259128)
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| Co-Investigator(Kenkyū-buntansha) |
NISHIYAMA Satoshi Geogyro, Principal Engineer, 技術研究所, 技師長
SANO Osamu Yamaguchi Univ., Dept.of Engineering Prof., 工学部, 教授 (20127765)
ANDO Masataka Kyoto Univ., DPRI, Prof., 防災研究所, 教授 (80027292)
KIYAMA Tamotsu Mitsui Construction, Principal Investigator, 技術研究所, 主任研究員
TSUKADA Kazuhiko Kyoto Univ., Dpt.of Engineering, Associate Prof. (10179971)
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| Project Period (FY) |
1998 – 1999
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| Keywords | P-wave velocity / Resistivity / strain / stress change / dipole-dipole method / water-injection experiment |
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| Research Abstract |
We have developed the integrated method to detect ultra-small changes in crustal stress, which is composed of simultaneous and precise measurements of Δ Vp (changes in velocity of ultrasonic-frequency P-wave), Δ R/R (changes in earth resistivity and Δ ε (changes in crustal strain). Using this integrated system, we have monitored the change in crustal stress at three distinctive sites, Mozumi Fault Observation Tunnel site, Aburatsubo Bay site, and Nojima Fault site.
The results of long-term observations are summarized as follows ;
1. Mozumi Fault Observation Tunnel site. Δ R/R is very sensitive to the environments in tunnel, and we must reinstall electrode into boreholes. The long-term build-up of stress was successfully detected via Δ Vp.
2. Aburatsubo Bay site. Both Δ R/R and Δ Vp can precisely sense the daily-changes in stress produced by ocean tide.
3. Nojima Fault site. In this site, we have injected pressurized water into borehole in the vicinity of fault. In order to monitor the stress changes produced in surrounding rocks via earth resistivity, we have developed new system (GPS synchronized ac-based system) adapted for dipole-dipole electrode configuration. On starting water injection, the resistivity immediately increased by about 2%, and was constant during water injection, and recovered the initial value at the reduction of pressure. The rectangular pulse-like increase in resistivity clearly suggests that the increase is not caused by the extension of water but by stress change in host rock.
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