Elastic wave velocity and electrical conductivity in a brine-saturated rock and microstructure of pores

Tohru Watanabe*, Miho Makimura, Yohei Kaiwa, Guillaume Desbois, Kenta Yoshida, Katsuyoshi Michibayashi

*この論文の責任著者

研究成果: ジャーナルへの寄稿学術論文査読

16 被引用数 (Scopus)

抄録

Elastic wave velocity and electrical conductivity in a brine-saturated granitic rock were measured under confining pressures of up to 150 MPa and microstructure of pores was examined with SEM on ion-milled surfaces to understand the pores that govern electrical conduction at high pressures. The closure of cracks under pressure causes the increase in velocity and decrease in conductivity. Conductivity decreases steeply below 10 MPa and then gradually at higher pressures. Though cracks are mostly closed at the confining pressure of 150 MPa, brine must be still interconnected to show observed conductivity. SEM observation shows that some cracks have remarkable variation in aperture. The aperture varies from ~ 100 nm to ~ 3 μm along a crack. FIB–SEM observation suggests that wide aperture parts are interconnected in a crack. Both wide and narrow aperture parts work parallel as conduction paths at low pressures. At high pressures, narrow aperture parts are closed but wide aperture parts are still open to maintain conduction paths. The closure of narrow aperture parts leads to a steep decrease in conductivity, since narrow aperture parts dominate cracks. There should be cracks in various sizes in the crust: from grain boundaries to large faults. A crack must have a variation in aperture, and wide aperture parts must govern the conduction paths at depths. A simple tube model was employed to estimate the fluid volume fraction. The fluid volume fraction of 10−4–10−3 is estimated for the conductivity of 10−2 S/m. Conduction paths composed of wide aperture parts are consistent with observed moderate fluctuations (< 10%) in seismic velocity in the crust.[Figure not available: see fulltext.].

本文言語英語
論文番号129
ジャーナルEarth, Planets and Space
71
1
DOI
出版ステータス出版済み - 2019/12/01

ASJC Scopus 主題領域

  • 地質学
  • 宇宙惑星科学

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