Finite Element Simulation of Present Crustal Deformation in the Southwest Tianshan Orogenic Belt

Objectives: As the youngest intra-land Cenozoic resurrected orogenic belt, the Tianshan region exhibits intricate tectonic deformation and frequent seismic activities, rendering it a natural laboratory for investigating continental dynamics. Through numerical simulations, our objective is to obtain stress accumulation patterns of major faults in the Tianshan region. By conducting numerical simulation experiments with individually loaded blocks, this study aims to analyze the respective roles of the Pamir Plateau and the Tarim Basin in the tectonic evolution of the southwest Tianshan. Methods: In this study, we constructed a three-dimensional elastic-viscoelastic finite element model of the Southwest Tianshan by incorporating GPS (Global Positioning System) observations as a constraint and considering the prominent active faults and layered lithospheric structure. Based on the finite element model, we simulated the crustal deformation field, the principal strain rate within the region, as well as stress accumulation rates of major active faults and their corresponding Coulomb stress change rates. Results: The simulation results indicate that the stress field in the Tianshan orogenic belt is dominated by the principal compressive stress in north-south direction, and the average strain rate inside the orogenic belt is 3.5×10^-8/a. The Keping, Maidan, and Nalati faults exhibit high rates of stress accumulation, indicating a significant likelihood of future strong earthquakes. Notably, the western section of the Keping fault demonstrates the most rapid increase in Coulomb stress, reaching up to 1.5 kPa/a. The results of individually loading experiments reveal that the tectonic deformation of the Tianshan to the east of the junction between the Tarim Basin and Pamir Plateau is primarily influenced by a combined extrusion force exerted by these two blocks. The Tianshan orogenic belt to the west of the junction is predominantly influenced by the extrusion of the Pamir Plateau, while the Tarim Basin plays a limited role. Conclusions: Through numerical simulations, we quantitatively derived the stress accumulation patterns of the major faults in the Tianshan region and revealed the potential dynamic mechanism underlying convergent deformation in the southwest Tianshan, thereby providing robust support for future seismic risk assessment of this area.