Exploring the Relationship between Strain Change in Fengjie Area of the Three Gorges Reservoir and Large Earthquakes on the Edge of the Sichuan Basin

This study investigates the relationship between near-surface crustal strain and large earthquakes by utilizing continuous observation data from a borehole strain instrument in Fengjie-Hongtu, located in the Three Gorges Reservoir area. The observation data was subjected to normalized processing and analysis, leading to the identification of three distinct and morphologically similar surface strain trend anomalies. These anomalies coincided with earthquakes of magnitude 6 or higher on the edge of the Sichuan Basin. In order to explore the reasons behind the anomalous changes in strain trends, geological research was combined with findings from the three earthquakes. The research results suggest that the surface strain trend anomalies observed in the Fengjie borehole strain may indicate alterations in the state of stress and strain transmission within the regional stress field. These three anomalies are preliminarily determined to be precursory anomalies. This finding is important for further understanding the mechanism of earthquake generation and early warning.