Home – Home – Jornals – Russian Geology and Geophysics 2025 number 6

The junction zones of mountain ranges with adjacent intramontane basins and foreland basins, developing under regional compression and transpression, are concentrators of key seismogenic faults. In this case, two counter-dipping systems of reverse faults and thrusts develop, which leads to the formation of positive (forebergs, pop-up structures, fault and tectonic scarps, and fault-related folds) and negative morphostructures (pop-down structures) in the marginal parts of sedimentary basins. As a result, the marginal parts of the basins are involved in the uplift. This results in the gradual growth and expansion of mountain ranges, accompanied by a corresponding reduction in the size of intramontane basins, indicating that the upper portion of the Earth’s crust experiences shortening. However, the mechanisms of occurrence of conjugate fault systems remain not fully understood. The mechanisms of such deformations in the upper crust are investigated under lateral compression of the rock mass using two-dimensional numerical modeling. The problem is solved in the elastic-plastic approximation using the Drucker-Prager-Nikolaevsky model with a non-associated flow law. In all models, regardless of the number of layers, reverse faults and thrusts with direct and reverse dips relative to the direction of horizontal compression are formed. As a result, positive and negative structures are formed in the model’s top surface relief, which are analogs of the corresponding natural morphostructures. The resulting data show that the development and configuration of localized shear bands corresponding to reverse faults and thrusts are affected by elastic-strength parameters, friction at the base of the model, and conditions on its lateral boundaries. It is revealed that, in the case of a multilayer medium, a single stage of deformations may result in a multitiered system of localized shear bands, characterized by different slopes and limited only by a specific layer. Special attention is paid to models that exhibit interlayer slipping, driven by varying relative movement rates of the layers due to differences in the elastic and strength properties of the rocks, thereby leading to the development of backthrusts in the upper part of the section that are not associated with the base of the model. Backthrusts are most often observed in the upper part of the model. Block inclusions at the base of the models, regardless of their strength properties, can affect the spatial localization of multidirectional localized shear bands that arise at their boundaries. The numerical modeling data allow for a better understanding of the relationship between the mechanical properties of rocks and sediments with the features of the development of faults, thrusts, and backtrusts.