Block motion, slip rates, and earthquake hazard assessment of boundary faults in the Sichuan–Yunnan region, China

Quantitative analysis of the slip rate of active faults and their seismic parameters is important for seismic hazard analysis. In this study, we first construct an elastic block model to obtain the slip rate of boundary faults based on the distribution characteristics of active faults, seismicity, and global navigation satellite system (GNSS) observations in Sichuan–Yunnan, China. Then, the long-term seismic risks of the boundary faults are quantitatively evaluated based on the principle of seismic moment balance. The Sichuan–Yunnan region can be divided into 17 relatively independent and stable subblocks. There is clear zoning in the distribution and mechanisms of boundary fault movement and deformation. The boundary faults exhibit an alternating dextral–sinistral–dextral–sinistral strike-slip pattern from northeast to southwest. Among these boundary faults, the Xianshuihe–Xiaojiang fault zone has a high sinistral strike-slip rate, and the Jinshajiang fault plays an important role in accommodating the movement and deformation of the subblocks in the Chuandian block. The dextral strike-slip rate is approximately 10 mm/yr, which is diffusely transferred to the secondary boundary faults in the Chuandian block. Comparison of the rates of moment accumulation and release reveals that the southern segment of the Xiaojiang fault, the Longriba fault, the Daliangshan fault, and the Yuanmou fault exhibit significant moment deficits, with corresponding moment magnitudes exceeding Mw 7.5. More attention should be given to the strong earthquake risks of these faults. The Xianshuihe–Xiaojiang, Jiali–Lancangjiang, and Red River faults, which are arc shaped, dominate the regional deformation and determine the motion and deformation model of the subblocks and secondary boundary faults within the Chuandian block and the area southwest of the Red River fault.