Gravity-anomaly-based analysis of surface ruptures along the Palu-Koro Fault (Indonesia) for long-term seismic hazard mitigation

Abstract

The Palu-Koro Fault system in Central Sulawesi is a major strike-slip fault associated with significant seismic hazards. This study investigates the fault dynamics and associated surface ruptures using gravity anomaly data and derivative-based geophysical methods. The Simple Bouguer Anomaly (SBA) values, ranging from –2 to 56 mGal, reveal substantial density contrasts in the subsurface, delineating fault boundaries and localised geological structures. Residual anomaly maps highlight sharp density gradients, which correspond to active fault zones. The derivative analyses, including First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD), further refine the fault geometry and movement mechanisms, confirming the predominantly strike-slip nature of the Palu-Koro Fault, with localised normal faulting in certain segments, particularly in pull-apart basins and fault stepovers. The identified fault structures are consistent with previously mapped surface ruptures and aftershock distributions, indicating a strong correlation between gravity-derived density contrasts and active fault segmentation. These findings offer critical insights into fault behaviour, contributing to more accurate seismic hazard assessments and disaster mitigation strategies. The results reinforce the importance of gravity-based geophysical techniques in fault characterisation and highlight their potential for integration with other geophysical datasets in seismic hazard analysis.