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\title{Shear-enhanced electrical conductivity of synthetic quartz-graphite
gouges: Implications for electromagnetic observations in carbonaceous
shear~zones}



\author[1]{Jinyu Chen}%
\author[1]{J. Chen}%
\author[1]{Lu Yao}%
\author[1]{Xi Ma}%
\affil[1]{Institute of Geology, China Earthquake Administration}%


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  \date{May 07, 2026}


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Abstract

Graphite is considered as a material that promotes fault weakening and
electrical conductivity (\selectlanguage{greek}\emph{σ}\selectlanguage{english}) enhancement at fault zones. We
studied how shear deformation may affect the evolution of friction and
electrical conductivity of synthetic quartz (Qz)-graphite (Gr) mixtures
and, more importantly, whether the \selectlanguage{greek}\emph{σ} \selectlanguage{english}of the mixtures present
visible changes at the beginning of the simulated fault slip.
Long-displacement friction experiments were performed on 1.2--2.3
mm-thick gouge specimens of varied Gr volume fraction
(\emph{X}\textsubscript{Gr} = 0--100 vol.\%) under identical normal
stress (2 or 5 MPa), slip rate (\textasciitilde{}1.0 mm/s), and
N\textsubscript{2}-flushing conditions. The experimental results
suggested that the \selectlanguage{greek}\emph{σ} \selectlanguage{english}of the specimens with [?] 4.6 vol.\%
\emph{X}\textsubscript{Gr} abruptly increased under limited shear
displacement. With continued shear, the steady-state electrical
conductivity (\selectlanguage{greek}\emph{σ}\selectlanguage{english}\textsubscript{ss}) increased by more than seven
orders of magnitude when \emph{X}\textsubscript{Gr} \textgreater{} 3.4
vol.\%, while the steady-state frictional coefficient remained high
(0.54--0.80) except for the specimens with \emph{X}\textsubscript{Gr}
\textgreater{} 13.6 vol.\%. The post-mortem microstructures revealed
that the high \selectlanguage{greek}\emph{σ}\selectlanguage{english}\textsubscript{ss} observed in the intermediate Gr
content specimens (3.4--13.6 vol.\%) is associated with an ad-hoc fabric
(graphite--cortex clasts) present in the principal slip zone. For high
Gr content, excess Gr flakes fill the pores and help develop
mechanically lubricated surfaces. We propose that low Gr content (i.e.,
as low as 3.4 vol.\%) can cause high conductivity anomalies in natural
shear zones. Overall, the findings suggest that the initiation of slips
within carbonaceous shear zones can be detected by identifying unusual
temporal signals using electromagnetic stations.

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