Modeling the effects of lateral loading on a bent strike-slip fault system: A case study from Palu-koro and Matano faults, Indonesia

Abstract

The Palu–koro and Matano faults form a major bent strike-slip fault system in central Sulawesi, Indonesia, accommodating significant crustal deformation associated with regional plate interactions. In this study, we investigate the mechanical response of this fault system using three-dimensional numerical modeling to evaluate how different lateral loading configurations influence fault slip and stress patterns. Dirichlet (displacement-rate) boundary conditions, inferred from regional plate velocities, are applied to the model domain at the x-face, y-face, and in combined x- and y-face configurations. Models with pure x-face or y-face loading generate lateral slip patterns that are mechanically compatible with idealized Riedel shear kinematics; however, the resulting slip sense differs from the present day tectonic motion of the Palu–koro and Matano faults. In contrast, models with combined boundary conditions reproduce first-order characteristics of the observed fault behavior. In particular, scenarios with dominant lateral loading at the x-face (e.g., 70% x-face and 30% y-face) produce predominantly sinistral slip along both faults and higher slip concentrations along the Palu–koro fault, consistent with tectonic and geodetic observations. The combined loading models also exhibit a subtle rotation of the maximum principal stress orientation from WNW–ESE along the Palu–koro fault to NE–SW along the Matano fault, which is qualitatively consistent with stress orientations inferred from focal mechanism inversions. Overall, the results suggest that combined regional lateral loading, with a dominant north–south lateral movement, provides a plausible mechanical framework for understanding deformation localization and stress rotation within the Palu–koro–Matano fault system.