論文

査読有り 筆頭著者
2019年10月

Identification of capable faults using fault rock geochemical signatures: A case study from offset granitic bedrock on the Tsuruga Peninsula, central Japan

Engineering Geology
  • Masakazu Niwa
  • ,
  • Koji Shimada
  • ,
  • Tsuneari Ishimaru
  • ,
  • Yoshihiro Tanaka

260
記述言語
英語
掲載種別
研究論文(学術雑誌)
DOI
10.1016/j.enggeo.2019.105235

© 2019 Elsevier B.V. The identification of capable faults is crucial for reliable seismic hazard assessments. To identify geochemical signatures characterizing recent, near-surface faulting, we analyzed the mineral and bulk-rock compositions of a range of fault rocks. We compare the compositions of two faults in central Japan that displace the same granitic unit, but record distinct geological histories: the capable Shiraki–Nyu Fault and a minor, incapable fault. Brownish gouge along the Shiraki–Nyu Fault (representing the principal slip surface) records MnO enrichment and FeO depletion and has a positive Ce anomaly, which was likely produced through oxidation reactions. Compositional mapping of outcrop and core samples from the Shiraki–Nyu Fault indicates that compositional changes (Mn- and Fe-oxide and/or oxyhydroxide precipitation along the principal slip surface) were driven by the fault-driven upward migration and oxidation of reduced fluids from depth to the near-surface. Mapping also indicates that Mn-rich gouge (and ultracataclasite) has undergone brecciation due to recent shallow-level faulting. In the Mn-rich gouge, Ce, Ba, and Y may have been enriched through co-precipitation and/or sorption onto the Mn oxide surfaces. Pale gray gouge from the principal slip surface of the minor incapable fault records no oxidation-related chemical changes. However, anastomosing/grid-like fractures filled with dark gray clay, which cut the pale gray gouge yield elevated MnO and Ba concentrations, low FeO concentrations and positive Ce anomalies, as well as high halloysite abundances. These chemical changes are attributed to post-faulting infiltration of oxidized surface water rather than repeated faulting. We show that geochemical analysis, combined with detailed geological observations, can be used to determine the spatial distributions of elements in heterogeneous fault zones, and contribute to the identification of recent, near-surface faulting events.

リンク情報
DOI
https://doi.org/10.1016/j.enggeo.2019.105235
URL
https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85070500008&origin=inward
ID情報
  • DOI : 10.1016/j.enggeo.2019.105235
  • ISSN : 0013-7952
  • SCOPUS ID : 85070500008

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