Three-dimensional distribution and hydrogeological properties of the Omagari Fault in the Horonobe area, northern Hokkaido, Japan

Ishii, Eiichi; Yasue, Ken-ichi; Tanaka, Takenobu; Tsukuwi, Routa; Matsuo, Kazunori; Sugiyama, K.; Matsuo, Shigeaki

doi:10.5575/geosoc.112.301

Cited by 28 publications

(3 citation statements)

References 20 publications

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“…A magnetotelluric survey showed several high-resistivity zones, one of which corresponds to the Omagari Fault as inferred from reflection seismic surveys. The highresistivity zones are correlated with bodies of lowsalinity water, which suggests that meteoric water has infiltrated through the permeable Omagari Fault zone (Ishii et al, 2006b).…”

Section: Outline Of Geology At Sampling Sitesmentioning

confidence: 97%

Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids

et al. 2010

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owing to interaction with the surrounding rocks. In several areas, fossil sea water was found to have δ 18 O values of +5 to +8‰ due to the oxygen isotopic shift caused by the interaction, but to retain almost the same Cl concentration as fresh sea water (e.g., Sakai and Matsubaya, 1974;Mizukami et al., 1977;Shibata et al., 2005).At depths below ca. 2 km in sedimentary regions associated with oil and/or natural gas, formation waters tend to be geopressured fluid with pressures between hydrostatic and lithostatic values (e.g., Myers, 1968;Jones, 1970;Oki et al., 1999;Xu et al., 2006). The δD and δ 18 O data show that most geopressured fluid can be explained as a mixture of fossil sea water and local meteoric water, with an oxygen isotope shift due to rock-water interaction. Recently, fluids that have oilfield-like characteristic, with unusually high δD (-20‰) and low Cl concentrations (ca. 6,000 mg/L) have been observed along faults in the Horonobe area (Ishii et al., 2006). These fluids might have originated as a mixture between sea water and Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids (Received July 14, 2009; Accepted June 7, 2010) Thermal and groundwaters are distributed along the west coast and in the inland region of Northwestern Hokkaido, Japan. The waters in the latter group have relatively high temperatures. Stable (D, O) and noble gas isotopic compositions of 23 thermal and groundwaters were analyzed to investigate their origins. The Cl concentrations vary from 45 to 19,300 mg/L and the δD values are in the range of -90 to -8‰. The δD-δ 18 O plots show a linear relationship which can be explained by a simple mixing of local meteoric waters and altered sea water, with oxygen isotopic shift of 5‰. However, a δD-Cl plot shows that there is also a contribution of an additional water component of different origin. This 3rd component has a δD value of -20‰ and Cl concentration of 6,000 mg/L. Multivariate statistical analysis of the observed chemical and isotopic compositions using the code M3 (M; multivariate mixing and mass balance) also supports the view that the Toyotomi thermal water has the composition closest to that of the 3rd groundwater component. This component is regarded as a geopressured fluid.The 3 He/ 4 He ratios in these waters are in the range of (0.1-5) × 10 -6 , which indicate contributions of both mantle and crustal He to the thermal and groundwaters in the studied area. The Toyotomi thermal water has a 3 He/ 4 He ratio of 5.5 × 10 -7 , and a high 3 He/ 20 Ne ratio (~700). These results indicate a crustal He input with a small amount of mantle-derived He and imply that the 3rd groundwater component is of deep origin. On the basis of isotopic and chemical compositions, 5 of 23 samples studied groundwater and thermal waters are contributed by a geopressured fluid component. The results show that geopressured fluids with a δD value of -20‰ and Cl concentration of 6,000 mg/L are widely distributed ...

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Section: Outline Of Geology At Sampling Sitesmentioning

confidence: 97%

Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids

et al. 2010

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“…In the Horonobe area, an NNW-SSE striking map-scale fault (Omagari Fault) is generally subparallel to major fold hinges in the area. The Omagari Fault possesses an E-W step-over at the surface that possibly converges at depth (Ishii et al, 2006). The Horonobe Underground Research Laboratory (URL) is located on the west side of the Omagari Fault (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

Formation mechanism of extension fractures induced by excavation of a gallery in soft sedimentary rock, Horonobe area, Northern Japan

Tokiwa

Tsusaka

Matsubara³

et al. 2013

Geoscience Frontiers

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a b s t r a c tThis paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan. Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone (EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks. The EDZ fractures terminate against pre-existing shear fractures. Therefore, even for excavations in soft sedimentary rocks, formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes.

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“…In the Horonobe area, a map-scale fault, the Omagari Fault, strikes NNW-SSE, generally subparallel to major folds in the area. The Omagari Fault is an oblique fault with reverse dip-slip and sinistral strike-slip components, and possesses an E-W step-over at the surface that possibly converges at depth [16].…”

Section: Geological Settingmentioning

confidence: 99%

Influence of a fault system on rock mass response to shaft excavation in soft sedimentary rock, Horonobe area, northern Japan

Tokiwa

Tsusaka

Ishii

et al. 2011

International Journal of Rock Mechanics and Mining Sciences

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Three-dimensional distribution and hydrogeological properties of the Omagari Fault in the Horonobe area, northern Hokkaido, Japan

Cited by 28 publications

References 20 publications

Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids

Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids

Formation mechanism of extension fractures induced by excavation of a gallery in soft sedimentary rock, Horonobe area, Northern Japan

Influence of a fault system on rock mass response to shaft excavation in soft sedimentary rock, Horonobe area, northern Japan

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