Response of shallow geostress to deep geostress and seismic hazard analysis before and after the Wenchuan and Lushan earthquakes

High stresses in the shallow section of the upper part of the active fault are usually considered as stress anomalies prior to the occurrence of strong earthquakes, while low stresses are safe regions. However, several earthquake cases have shown that the seismic hazard in the low-stress state has multiple solutions. To further explore the characteristics of stress anomalies before strong earthquakes, this study uses the ground stress measurements and the b-values of seismic activity parameters before the 2008 Wenchuan MS8.0 earthquake and the 2013 Lushan MS7.0 earthquake to establish a model for the response of shallow stress to deep stress, based on the consideration of the intensity of the influence of deep stress on shallow stress, and to investigate the relationship between different stress states before strong earthquakes. The relationship between different stress states and seismic hazard before the occurrence of strong earthquakes is discussed. The results show that: low b-values on the upper plate of the active fault corresponding to shallow high ground stress are potential seismic hazard zones, while those corresponding to low ground stress are seismic hazard uncertainty zones, which need to be confirmed with more studies; the low stress state before the 2008 Wenchuan MS8.0 earthquake may reflect the existence of strong regional stress adjustment. This study has implications for understanding the shallow stress state of faults to assess the seismic hazard of faults. © 2023 Geological Society of China. All rights reserved.