Stress evolution on active faults in the southwestern Yunnan region, southeastern Tibetan Plateau, and implications for seismic hazard

Abstract

Southwestern Yunnan is expressed as a seismically active region bordering the southeastern Tibetan Plateau. However, the recent seismicity in this region has been relatively quiet. Considering some highly-populated cities nearby and the historical record in this region, understanding the stress changes on the main active faults is crucial for seismic hazard analysis. In this study, we calculated the co- and post-seismic Coulomb failure stress change (ΔCFS) on these faults caused by historical earthquakes in and around the region. Then, by integrating the inter-seismic tectonic loading estimated using a geodynamic model and GPS data, we analyzed the total stress change on all of these faults. The results reveal that the ΔCFS patterns caused by events on different segments of the Sagaing Fault vary; the combined ΔCFS increased on the middle segment of the Longling-Lancang Fault, the Heihe Fault, and the Nantinghe Fault, among which the maximum change reached 3.5 kPa. The great 1950 Assam earthquake in the eastern Himalayan syntax increased the ΔCFS on almost all faults, and the maximum change reached 20 kPa. More importantly, the ΔCFS caused by earthquakes in the southwestern Yunnan region was significantly larger than that caused by earthquakes in the surrounding region because of the geographical proximity. The inter-seismic tectonic stress loading rate reached 2 kPa.yr−1. A significant total stress build-up occurred on five segments distributed among four faults, namely, the Nantinghe Fault, the Longling-Lancang Fault, the Heihe Fault, and the Menglian Fault, making them possible candidates for the next major earthquake in this region.