Gravity-based structural analysis of the Liwa segment of the Sumatra fault system (SFS) using derivative techniques and 3D density modelling

Heri Dwi Marsanti; Mikael Syväjärvi

doi:10.58524/cesl/v1i1.118

Authors

Heri Dwi Marsanti Department of Physics, Institut Teknologi Sumatera Author
Mikael Syväjärvi Alminica AB, Ulrika, Östergötlands Län Author

DOI:

https://doi.org/10.58524/cesl/v1i1.118

Keywords:

Gravity anomaly, Subsurface fault structure, First horizontal derivative, Second vertical derivative, Sumatra fault system

Abstract

Liwa, Krui, and the surrounding areas in western Lampung, Indonesia, are highly susceptible to geological hazards, particularly earthquakes and landslides. The seismic activity in this region is strongly associated with the Sumatra fault system (SFS), a major strike-slip fault that accommodates the oblique convergence between the Indo-Australian and Eurasian plates. This study aims to identify and characterize subsurface fault structures using gravity data derived from TOPEX satellite observations. The analysis was conducted through two-dimensional (2D) and three-dimensional (3D) gravity modeling based on the Complete Bouguer Anomaly (CBA) data obtained from the processed free-air gravity anomalies. To enhance structural interpretation, derivative techniques including the First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) were applied to delineate density contrasts associated with fault boundaries. The results of the derivative analyses indicate the presence of significant structural discontinuities that correspond to fault zones trending northwest–southeast, consistent with the regional orientation of the Sumatran Fault System. The interpreted gravity anomalies suggest the existence of uplifted and down-dropped blocks forming horst and graben structures across the Liwa–Krui region. The 2D subsurface models reveal pronounced density contrasts that mark the structural boundaries controlling regional tectonics. Furthermore, the 3D density distribution model indicates shallow low-density materials (1.0–1.5 g/cm³) at depths of 0–0.63 km, which are interpreted as unconsolidated alluvial deposits. In contrast, higher density values reaching approximately 3.0 g/cm³ at depths between 2.74 and 5.53 km are interpreted as consolidated bedrock units.

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