Seismic hazards along the Longmen Shan fault: Insights from stress transfer between major earthquakes and regional b value

Abstract

Abstract There are two seismic gaps (Dayi seismic gap and Tianquan-Kangding seismic gap) on the Longmen Shan fault (LMSF), despite the successively occurrence of the 2008 Mw7.9 Wenchuan and 2013 Mw6.6 Lushan earthquakes. To analyze the effects of the Wenchuan and Lushan earthquakes on the LMSF (especially on seismic gaps along the LMSF) and regional seismic hazards, we calculate Coulomb stress changes caused by the Wenchuan and Lushan earthquakes based on a three-dimensional viscoelastic finite element model. We also calculate the spatial distribution of regional b value based on the instrumental seismic catalog before Wenchuan earthquake, and infer the regional background stress level according to the inverse correlation between b value and stress level. The results show that regional earthquakes (including the 2008 Mw7.9 Wenchuan earthquake, 2013 Mw6.6 Lushan earthquake, 2014 Mw6.1 Kangding earthquake, 2017 Mw6.5 Jiuzhaigou earthquake and 2022 Mw6.6 Luding earthquake) occurred in regions with low b value. Meanwhile, subsequent earthquakes occurred in regions where Coulomb stress changes caused by the Wenchuan and Lushan earthquakes are positive. This suggests that regions with both low b value and positive Coulomb stress changes may pose higher seismic hazards. There are five regions (southern Xianshuihe fault, southernmost segment of LMSF, Dongkunlun fault, northern Xiaojinhe fault, and Hanan-Qingshanwan fault) with both high Coulomb stress changes caused by the Wenchuan and Lushan earthquakes and low b value, which may indicate high-stress accumulation and high seismic hazard in the future. The results also show that Coulomb stress changes caused by the Wenchuan and Lushan earthquakes increased significantly in the Dayi seismic gap (+ 0.214 ~ + 2.606 MPa), and Tianquan-Kangding seismic gap (+ 0.016 ~ + 0.205 MPa), while the result of high b value for the Dayi seismic gap and the northern-central segment of Tianquan-Kangding seismic gap indicates less background stress accumulation. With tectonic loading continues, seismic hazards on both seismic gaps should cause our attention.