Present-day stress field in Sichuan-Yunnan region based on comprehensive updated earthquake focal mechanisms catalog

The Sichuan-Yunnan region of the SE and E margin of the Tibetan Plateau, situated at the transitional nexus between the seismically-active intensely-deformed Tibetan Plateau and the tectonically stable Yangzi block with comparatively low seismicity, has experienced substantial geological transformations during the Quaternary. Given the pronounced seismicity, there is an escalating imperative for an accurate and refined distribution of the stress field in the region. To unravel the contemporary stress state within major active blocks and along active faults in the study area, an elaborate computation of their tectonic stress field is undertaken by comprehensive updated earthquake focal mechanisms catalog. The tectonic stress field in Sichuan-Yunnan region exhibits obvious lateral variations, with the principal compressive stress direction demonstrating a notable correlation with the azimuth of the P axis. The directions of the stress field show a variation from north to south at ~ 28°N. The directions of the maximum and minimum principal compressive stress in the north show nearly E-W compression and N-S tension, respectively. Conversely, in the south, there is a discernible clockwise rotation trend from east to west. Localized normal faulting stress regimes are observed in the middle section of Xianshuihe fault and southwest side of Litang fault. The extensional environment of the former may be attributed to the tectonic activities such as block translation, clockwise rotation and vertical uplift, as well as the clockwise rotation of the Xianshuihe fault from NW-SW to NNW-SSE. The latter may be related to the extensional structures, rift basins and the normal fault movements in the crust formed by the detachment of the plates and delamination of the mountain roots at the end of Triassic. We also found that the tectonic stress field under the large faults, such as Longmenshan fault, Red River fault, Xiaojiang fault and Lijiang-Xiaojinhe fault, show segmented variation. The findings yield invaluable insights into the intricate dynamics of tectonic deformation along the SE margin of the Tibetan Plateau [supported by NSFC Projects 42330311, 42074065 & 41730212].