Numerical analysis of the seismic hazard in Sichuan-Yunnan region

    The Sichuan-Yunnan region is located in the southern part of Chinese north-south seismic belt and has strong seismic activity. The prediction of future strong earthquake activity in this region has always been a research hotspot. In this study, firstly, we established a quasi-three-dimensional finite element elastic model, combined with the regional geological background and GPS observation data. Then, based on the information of 30 M>6.7 historical earthquakes that occurred in the region over the past 100 years, and constrained by the Coulomb-Mohr rupture criterion, we inverted a possible reasonable initial stress field at a specific time. Secondly, we simulated the development process of each historical earthquake and reproduced the 30 events orderly, by comprehensively considering the tectonic stress loading in the seismogenic stage and the stress change in the co-seismic adjustment stage. However, it is worth noting that there were some uncertainties in the numerical simulation process. We used Monte Carlo random experiments to obtain 5000 kinds of different possible initial values, which all can reproduce the development process of historical events. Then we got different current reginal stress values and calculated earthquake risk coefficient. Finally, we used mathematical methods to investigate the current seismic hazard of the different models, and assembled them into a probability distribution map of possible seismic risk in the region. The preliminary result shows that the seismic risk in the rupture zone of historical earthquakes is greatly reduced, which means relatively safe. Mainly due to the stress change caused by the 2008 Wenchuan Ms8.0 earthquake, the seismic probability in the northeastern segment of the Longmenshan fault is as high as 30%. At the junction of the southwestern section of the Longmenshan fault and the Xianshuihe fault zone, the seismic probability is about 15-20%. In addition, near the Longling Ruili fault and the Lancangjiang fault in southwestern Yunnan, the value is about 10-15%. In recent years, small earthquakes have occurred frequently in southwestern Yunnan, and the seismic risk in this area is also worth noting.