Is clustered seismicity an indicator of regional stress? Insights from earthquake sequences in Yongning-Luguhu faulted basin, Southwest China

Using hypocenter relocation, moment tensor inversion, stress field inversion, and fault slip tendency analysis, this study systematically investigated three M5.5–5.8 earthquake sequences that occurred after 2000 in the Yongning-Luguhu faulted basin in the middle of the Lijiang-Xiaojinhe fault zone within the Sichuan-Yunnan block, Southwest China. Our results show that since the 2008 Wenchuan Earthquake, the tectonic stress pattern in this area may have changed and that b-values estimated for the earthquake sequences show evidence of an increasing trend in stress in the study area. Seismicity in the small-scale faulted basin adjacent to the large-scale fault zone is a possible indicator of regional stress. We also note that the aftershocks of the M5.7 earthquake sequence in 2012 and the M5.5 earthquake sequence in 2022 show relatively clear fluid diffusion-triggering characteristics. Overpressure of deep fluids is still the main factor driving seismic activity in the region, and we propose that the background tectonic stresses have not yet reached critical levels.