Modelling the interactions of discrete inherited structures, pervasive fabrics and extension direction during rifting: application to the Cenozoic Eger Graben

Abstract. Pre-existing mechanical heterogeneities significantly influence the evolution of continental rifts and their resulting fault architecture. The Cenozoic Eger Graben (EG) in the northwestern Bohemian Massif (Central Europe) represents a fossil rift system in which the role of structural inheritance has been relatively unaddressed. This study examines how basement structures inherited primarily from Paleozoic geodynamic events may have controlled syn-rift fault development in a setting where the orientation of the rift axis and basement fabric varied in space relative to the extension direction. Two series of crustal-scale analogue models inspired by the EG setting were designed to investigate the effects of both discrete and pervasive weaknesses on evolving fault populations. The first series simulated reactivation of a segmented basement weakness (velocity discontinuity, VD) under uniform or changing extension directions, testing an existing two-phase extension model. The second employed a uniformly extending elastic model base and approximated the role of pervasive fabrics by imprinting grooved patterns into the basal silicone layer. Surface strain evolution was analysed using digital image correlation, while final fault patterns were compared with the generalised structure of the EG. The results highlight the dominant influence of the initial extension phase during polyphase rifting, with the segmented geometry of the VD exerting further control on fault development. Some two-phase scenarios reproduce the observed fault pattern more successfully than others, suggesting that temporal variations in paleostress orientation remain plausible. However, experiments involving spatially variable basement fabrics demonstrate that faults of contrasting orientation and geometry can develop simultaneously above suitable inherited structures. Several structural features of the Eger Graben may therefore reflect synchronous reactivation of different inherited structures rather than rotation of the extension direction. The influence of pervasive fabrics on modelled fault geometries compares well with natural examples and demonstrates the broader applicability of this experimental approach.