Fault rocks and past to recent fluid characteristics from the borehole survey of the Nojima fault ruptured in the 1995 Kobe earthquake, southwest Japan

Ohtani, Toshio; Fujimoto, Koichiro; Ito, Hisao; Tanaka, Hidemi; Tomida, Naoto; Higuchi, Takayuki

doi:10.1029/2000jb900086

Cited by 78 publications

(62 citation statements)

References 25 publications

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“…Drilling studies have taken place in response to earthquakes of M w = 6.9-9.0 in Japan, Taiwan, China and the USA 8,[10][11][12][18][19][20][21] , and the results do not reveal anomalous temperatures or fluid pressures (Fig. 1).…”

mentioning

confidence: 94%

Extreme hydrothermal conditions at an active plate-bounding fault

Sutherland

Townend

Toy

et al. 2017

Nature

110

174

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mentioning

confidence: 94%

Extreme hydrothermal conditions at an active plate-bounding fault

Sutherland

Townend

Toy

et al. 2017

Nature

110

174

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“…The internal structure of the Nojima fault was described in detail in Ohtani et al (2000) and Tanaka et al (2001) and we provide a brief summary here. The lithology is mostly Cretaceous granodiorite with some porphyry dikes.…”

Section: Outline Of the Fault And Core Geologymentioning

confidence: 99%

Borehole water and hydrologic model around the Nojima fault, SW Japan

et al. 2007

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(1)Faculty of Education, Tokyo Gakugei University, Tokyo Japan (2)Central Research Institute, Mitsubishi Materials Corporation, Saitama, Japan (3)Department of Civil Engineering, Gifu University, Gifu, Japan (4)GSJ, AIST, Tsukuba, Japan (5)Department of Earth and Planetary Sciences, University of Tokyo, Tokyo, Japan (6)LGIT, CNRS, Grenoble, France koichiro@u-gakugei.ac.jp/ Fax: +81-42-329-7539Key words: carbonate, stable isotope, water-rock interaction, geochemical speciation -2 - AbstractThe active fault drilling at Nojima Hirabayashi after the 1995 Hyogoken-nanbu (Kobe) earthquake (M JMA = 7.2) provides us with a unique opportunity to investigate subsurface fault structure and the in-situ properties of fault and fluid. The borehole intersected the fault gouge of the Nojima fault at a depth interval of 623m to 625m. The lithology is mostly Cretaceous granodiorite with some porphyry dikes.The fault core is highly permeable due to fracturing. The borehole water was sampled in 1996 and 2000 from the depth interval between 630 and 650 m, just below the fault core. The chemical and isotopic compositions were analyzed. Carbon and oxygen isotope ratios of carbonates from the fault core were analyzed to estimate the origin of fluid.The following conclusions were obtained. (1) The ionic and isotopic compositions of borehole water did not change from 1996 to 2000. They are mostly derived from local ground water as mentioned by Sato and Takahashi (2000). (2) Geochemical speciation revealed that the borehole water was derived from a relatively deep reservoir, which may be situated at a depth of 3 to 4 km where the temperature is about 80-90 ˚C. (3) The shallower part of the Nojima fault (shallower than the reservoir depth) has not been healed from the hydrological viewpoints 5 years after the event, in contrast to the rapid healing detected by S wave splitting (Tadokoro and Ando, 2002). (4) Precipitation of calcite from present borehole water since drilling supports the idea of precipitation of some calcite in coseismic hydraulic fractures in the fault core (Boullier et al., 2004). (5) Carbon and oxygen isotope ratios of calcite indicated that the meteoric water flux had been localized at the fault core. (6) A difference in the carbon isotope ratio between the footwall and the hangingwall suggests that the fault has been acted as a hydrologic barrier, although the permeability along the fault is still high.

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“…While the strength of the undeformed and unaltered protolith of the Nojima fault is around 400 MPa at an effective confining pressure of 50 MPa, samples located at 14.5 m and 5 m from the fault plane have a 200 MPa and 150 MPa strength, respectively (Lockner et al, 2009). Thus, the residual stresses accumulated in the studied NOJ220 sample are close to that of the damaged granodiorite and could have contributed to the 30 enlargment of the observed 45m wide damage zone (Ohtani et al, 2000a ;Tanaka et al, 2001). …”

Section: Implications For the Development Of The Damage Zonementioning

confidence: 97%

“…The NOJ220 sample studied in this paper is located at 51.3 m from the main Nojima fault, that is outside the fault zone determined on the basis of studies of the drillcore samples (Ohtani et al, 2000a;Tanaka et al, 2001). Deformation microstructures corresponding to a low strain are nevertheless present in the thin section.…”

Section: Interpretation and Discussion 25mentioning

confidence: 99%

“…The drillhole sampled the Principal Slip Zone (PSZ) of the Kobe earthquake at 624.5 m depth (Fig. 1b;Ohtani et al, 2000a;Tanaka et al, 2001). Two major periods of seismic activity on the fault separated by an exhumation of the basement of the Awaji Island were inferred using the relationships between hydrothermal minerals and deformation 25 microstructures (Boullier et al, 2004a).…”

Section: Geological Settingmentioning

confidence: 99%

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High stresses stored in fault zones: example of the Nojima fault (Japan)

Boullier¹,

Robach²,

Ildefonse³

et al. 2017

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Abstract. During the last decade pulverized rocks have been described on outcrops along large active faults and attributed to damage related to a propagating seismic rupture front. Questions remain on the maximal lateral distance from the fault plane and maximal depth for dynamic damage to be imprinted in rocks. In order to document these questions, a core sample of granodiorite located at 51.3 m from the Nojima fault (Japan) that was drilled after the Hyogo-ken Nanbu (Kobe) earthquake is studied by using Electron Back-Scattered Diffraction (EBSD) and high resolution X-ray Laue 15 microdiffraction. Although located outside of the Nojima damage fault zone and macroscopically undeformed, the sample shows pervasive microfractures and local fragmentation that are attributed to the first stage of seismic activity along the Nojima fault characterized by laumontite as the main sealing mineral. EBSD mapping was used in order to characterize the crystallographic orientation and deformation microstructures in the sample, and X-ray microdiffraction to measure elastic strain and residual stresses in a quartz grain. Both methods give consistent results on the crystallographic orientation and 20show small and short wave-length misorientations associated with laumontite-sealed microfractures and alignments of tiny fluid inclusions. Deformation microstructures in quartz are symptomatic of the semi-brittle faulting regime, in which low temperature brittle, plastic deformation and stress-driven dissolution-deposition processes occur conjointly.Residual stresses are calculated from elastic strain measured by X-ray Laue microdiffraction and stress peaks at 100 MPa (mean 141 MPa). Such stress values are comparable to the peak strength of a damaged granodiorite from the damage zone 25 of the Nojima fault indicating that, although apparently macroscopically undeformed, the sample is actually highly damaged. The homogeneously distributed microfracturing of quartz is the microscopically visible imprint of this damage and suggests that high stresses were stored in the whole sample and not only concentrated on some crystal defects. It is proposed that the high residual stresses are the sum of the stress fields associated with individual dislocations, dislocation microstructures and originated from the dynamic damage related to the propagation of rupture fronts or seismic waves 30 associated to M6 to M7 earthquakes during Paleocene on the Nojima fault at a 3.7 -11.1 km depth (laumontite stability domain) where confining pressure prevented pulverization. The high residual stresses and the deformation microstructures Solid Earth Discuss., https://doi

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Fault rocks and past to recent fluid characteristics from the borehole survey of the Nojima fault ruptured in the 1995 Kobe earthquake, southwest Japan

Cited by 78 publications

References 25 publications

Extreme hydrothermal conditions at an active plate-bounding fault

Extreme hydrothermal conditions at an active plate-bounding fault

Borehole water and hydrologic model around the Nojima fault, SW Japan

High stresses stored in fault zones: example of the Nojima fault (Japan)

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