2006 Fiscal Year Final Research Report Summary
Estimates of Fault Strength, Frictional Heat, and Energy for the Chi-Chi, Taiwan Earthquake
| Project/Area Number |
16253003
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
Solid earth and planetary physics
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
MORI James Jiro Kyoto University, DPRI, Professor, 防災研究所, 教授 (50314282)
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| Co-Investigator(Kenkyū-buntansha) |
ITO Hisao JAMSTEC, CDEX, Associate Director, 地球深部探査センター, 科学計画室長 (10356470)
SHIMAMOTO Toshihiko Kyoto University, Graduate School of Science, Professor, 理学研究科, 教授 (20112170)
MATSUBAYASHI Osamu AIST, Institute for Geo-resources and environment, Group Leader, 地圏資源環研究部門, 研究グループ長 (70358034)
TANAKA Hidemi The University of Tokyo, Graduate School of Science, Lecturer, 理学系研究科, 講師 (40236625)
YABE Yasuo Tohoku University, Graduate School of Seience, Research Associate, 理学研究科, 助手 (30292197)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Frictional Heat / Chelungpu Fault / Taiwan / Temperature / Borehole / Chi-Chi Earthquake / Earthquake |
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| Research Abstract |
The main purpose of this project was to look for a temperature anomaly associated with faulting from the 1999 Chi-Chi, Taiwan earthquake (Mw7.6) on the Chelungpu fault. Any temperature change across the fault would give an estimate of the frictional heat produced at the time of the earthquake. Determining the level of frictional heat adds valuable information to a long-standing problem in seismology about the absolute stress levels and strengths of faults during large earthquakes. For the temperature measurements we able to use the Taiwan Chelungpu fault Drilling Project (TCDP) borehole which penetrated the fault at a depth of about 1100 meters in a region of large slip.
Using a high-resolution borehole instrument developed in this project, we measured continuous temperature profiles in the borehole in September 2005. The results, which were obtained 6 years after the earthquake, showed a small increase of temperature across the fault. This small temperature signal is interpreted as the residual frictional heat from the time of the earthquake. The modeled temperature data showed that a shear stress level of 0.8 to 1.7 MPa on the fault during the rupture. This value corresponds to an apparent coefficient of friction of 0.08 to 0.1, which is a very low value. If this is a representative value for the area of large faulting, significant low friction mechanisms are needed to explain the faulting.
Material properties, such as variations in heat conductivity, may affect the interpretation of the temperature signal. Investigating these effects is the purpose of a follow-up project. Other studies in the project investigated physical properties of the fault zone from the borehole cores and a water pumping test was done to determine the fluid flow properties.
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