Compilation of a focal mechanism solution database and investigation of the regional crustal stress field in the southeastern margin of the Tibetan Plateau

The southeastern margin of the Tibetan Plateau lies within the oblique convergence zone of the India-Eurasia collision. Since the Cenozoic, this region has experienced intense crust-mantle interactions, active tectono-magmatic processes, and complex focal mechanisms, reflecting a crustal structure with pronounced vertical layering and lateral segmentation. To better understand the regional stress regime and fault activity, we compiled a comprehensive database of focal mechanism solutions for the southeastern Tibetan Plateau. We collected and integrated earthquake data from 1950 to 2023 across the Sichuan-Yunnan region and adjacent areas. After data cleaning and integration, a database of 9902 high-quality focal mechanism solutions was established. Using a damped stress inversion method, we derived regional stress field models on 1°×1° and 0.2°×0.2° grids. The results reveal that: (1) focal mechanism types exhibit significant spatial heterogeneity; strike-slip events dominate the region, thrust events concentrate along the Longmenshan fault zone, and normal faulting prevails along the western boundary of the Sichuan-Yunnan block. (2) The large-scale stress field shows a systematic clockwise rotation of the maximum compressive stress axis (σ1) from north to south, consistent with the far-field effect of the ongoing India-Eurasia collision. (3) The high-resolution results reveal multi-scale stress variations, with strong horizontal continuity of σ1 across the plateau, supporting a long-term stable compressional regime. In contrast, higher three-dimensional complexity occurs along the block boundaries and southern Yunnan, particularly across the Lijiang-Xiaojinhe fault, where a clear north-south stress gradient is observed. This study provides the first systematic stress field characterization based on a unified focal mechanism database for the southeastern Tibetan Plateau, offering refined constraints on crustal deformation and insights into the geodynamic processes governing continental earthquake generation.