Evaluating the Utility of b-Value for Discriminating Foreshocks and Mainshocks in Yunnan, southwest China

Determining mainshocks from an ongoing seismic sequence poses a challenge for real-time hazard assessment. This study aims to address this issue by analyzing temporal variations in the b-value derived from the Gutenberg-Richter law, with a focus on moderate-to-large events in Yunnan province, southwest China. Yunnan is well known to experience frequent earthquakes due to the convergence of the Indian and Eurasian tectonic plates, along with its complex subsurface geological structure and active fault zones. Earthquake data were analyzed from the Unified National Catalog over the period from January 2000 through December 2022 and the magnitude of completeness is 1.4. We selected seismic sequences where the mainshock magnitudes were above 5. We employed a temporal b-value calculation approach, utilizing a minimum of 10 years of seismic data and including earthquakes within 20 km from the mainshock hypocenter. We used the long-term average b-value preceding the mainshock as the reference. Specifically, we compared the temporal b-value variation calculated for the one-month period following each mainshock to the reference b-value. In total, we investigated 23 sequences in the region. The b-value increased by 10% or more for 4 sequences and by <10% for 3 sequences. Three sequences showed b-value reduction. Insufficient data prevented analysis of 13 other sequences. To conclude, assessing temporal b-value variations is an active research topic to evaluate ongoing earthquake sequences. By testing the application in Yunnan, our b-value is able to help us identify a few mainshock-aftershock sequences. However, we also observe controversial cases. This limitation poses challenges to rapidly determine mainshocks in operational decision-making applications.