Delineation of shallow fault structures along the Sianok segment of the Sumatra fault using dipole–dipole electrical resistivity imaging

Gabriella A Sihite; Alamta Singarimbun; Marjiyono; Ahmad Said

doi:10.58524/cesl.v1i1.100

Authors

Gabriella A Sihite Department of Physics, Institut Teknologi Sumatera Author
Alamta Singarimbun Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Author
Marjiyono Centre for Geological Survey, Energy and Mineral Resources Ministry Author
Ahmad Said Friedrich-Schiller-University Jena Author

DOI:

https://doi.org/10.58524/cesl.v1i1.100

Keywords:

Sumatra Fault, Sianok segment, ERT, Dipole–dipole, Fault damage zone, Hazard assessment

Abstract

The Sianok segment of the Sumatra Fault is an active tectonic structure that plays a critical role in controlling seismic hazards in West Sumatra, Indonesia. Despite its significance, detailed information on the shallow subsurface characteristics of this fault segment remains limited, particularly regarding the spatial variability of fault-related deformation near the surface. This study applies high-resolution two-dimensional electrical resistivity tomography (ERT) using a dipole–dipole configuration to delineate shallow fault structures along the Sianok segment. Seven ERT profiles were acquired across locations selected based on lineament interpretation from Digital Elevation Model (DEM) data that intersect the mapped trace of the Sumatra Fault. The resistivity data were inverted using a smoothness constrained least-squares algorithm implemented in Res2Dinv to generate two-dimensional subsurface resistivity models. The resulting sections reveal pronounced lateral resistivity contrasts, disrupted stratigraphic patterns, and localized resistivity anomalies interpreted as fault-related deformation zones. The identified fault zones exhibit a wide range of resistivity values, from approximately 7.6 to 29,684 Ωm, reflecting variations in lithology including clay, sand, alluvium, tuffaceous sandstone, sandstone, and volcanic tuff. Interpretation of the resistivity sections indicates the presence of both steeply dipping and westward-inclined fault geometries across different profiles. Several lines display resistivity patterns consistent with vertical displacement associated with normal faulting, while others show features indicative of strike-slip–related deformation. The spatial correspondence between subsurface resistivity anomalies and DEM-derived lineaments provides independent validation of the surface expression of the Sianok segment and confirms the presence of shallow fault structures along all investigated profiles. This study demonstrates that dipole–dipole ERT, when guided by geomorphological lineament analysis, is an effective method for resolving shallow fault architecture in complex volcanic–sedimentary terrains. The results provide new quantitative constraints on the shallow subsurface expression of the Sianok segment of the Sumatra Fault, contributing to improved fault characterization and regional seismic hazard assessment.

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