Evaluating the role of convergence angle in the geometry of contractional and extensional strike-slip duplexes using 3D finite element models

Abstract

Strike-slip faults are fundamental tectonic structures that exert a major influence on both seismic activity and hydrocarbon reservoir development. However, the geometric evolution and internal deformation mechanisms of contractional and extensional strike-slip duplexes remain poorly understood. This study employs five three-dimensional finite element models in Abaqus to investigate how variations in the convergence angle of the main strike-slip fault control the geometry, deformation pattern, and stress distribution within duplex systems. The results demonstrate that fault-scarp development and internal deformation are strongly governed by the convergence angle and by the presence of duplex structures. The most pronounced geometric changes occur at zero-degree convergence, where displacement is parallel to the fault plane, producing dominant pure-shear deformation rather than simple shear. The strain ellipse patterns in both extensional and contractional duplexes correspond closely to those of transtensional and transpressional strike-slip zones. The models also show that oblique convergence and duplex formation significantly amplify local stress and strain concentrations, indicating that duplexes can act as potential sites of rupture initiation. Moreover, under identical geological conditions, contractional and extensional duplexes reach critical stress levels earlier than simple strike-slip faults, implying shorter earthquake recurrence intervals. These findings advance the understanding of scarp formation, deformation partitioning, and stress localization in strike-slip duplexes, with important implications for seismic hazard assessment and for predicting hydrocarbon migration and entrapment in structurally complex fault systems.