The southwestern margin of the Sichuan basin, particularly the Changning region, is characterized by highly complex geological structures with intricate and variable geometries. The dominant tectonic unit is the Changning–Shuanghe anticline, and the direction of the maximum principal stress is NWW-SEE. The structure of the anticline is broad in the east and narrow in the west, and is further dissected by secondary folds and faults. Historically, background seismicity in this region was relatively weak, with magnitude of most events below 3.0. However, in recent years, the area has experienced frequent moderate-to-strong earthquakes. For instance, on 16 December 2018, an M_S5.7 earthquake struck Xingwen County, Sichuan, causing multiple injuries and widespread secondary disasters. Subsequently, on 17 June 2019, the region experienced the largest earthquake ever recorded in its seismic history—the Changning M_S6.0 event, which filled the long-standing absence of earthquakes exceeding magnitude 6.0 in this area and was followed by numerous aftershocks above magnitude 5.0. This sequence has made Changning one of the most seismically active regions within the Sichuan basin, drawing broad attention from both the scientific community and the public.

Despite these developments, most existing studies have emphasized single-parameter analyses （e.g., stress field or seismicity） and have seldom conducted integrated investigations of multiple factors. In particular, comprehensive studies jointly examining source parameters and seismic activity to elucidate the regional stress evolution remain limited. To address this gap, the present study investigates earthquakes with M_S≥3.0 that occurred between October 2010 and July 2022 in the Changning area （104.6°E−105.2°E, 28°N−28.5°N）. We employ the CAP full-waveform inversion method to derive focal mechanism solutions and apply the damped least-squares inversion to resolve regional stress field characteristics. In addition, we extract key source parameters such as stress drop and corner frequency through a multi-taper spectral inversion approach. By combining these parameters with the spatiotemporal evolution of the b-value, we systematically explore the coupling mechanisms between seismic activity, industrial operations, and tectonic stress perturbations. The ultimate objective is to clarify the seismogenic processes and dynamic evolution of stress, thereby providing a scientific basis for seismic hazard assessment in southern Sichuan.

The results demonstrate that the dominant focal mechanisms are thrust-faulting and strike-slip types, with epicenters mainly concentrated on the western margin of the tectonically active zone. The stress field inversion indicates that the maximum principal stress is oriented NWW–SEE, consistent with the extrusion regime of the eastern Qinghai-Xizang Plateau. Although the regional stress field is generally stable, a short-term disturbance occurred following the 2019 mainshock. Temporal variations in b-value and stress drop exhibit a stage-wise coupling, reflecting a three-phase stress evolution cycle of “loading–release–reloading.” Specifically, the period of 2010−2014 corresponds to a loading stage; 2015−2019 represents a release stage characterized by frequent ruptures; and the post-2019 period indicates reloading, during which stress gradually recovered and the b-value stabilized （Fig. 2）. The stress inversion results （Fig. 7） broadly agree with the background tectonic regime, further supporting the interpretation that most earthquakes （primarily thrust and strike-slip events） in the region are governed by the regional stress field.

Furthermore, clear correlations are identified between source parameters and earthquake magnitude: stress drop and source radius increase with magnitude, whereas corner frequency decreases, implying that larger earthquakes correspond to greater rupture dimensions and enhanced energy releases. Integrated analysis suggests that the evolution of source parameters and seismicity in the Changning region is controlled primarily by two factors. First, the complex and densely distributed fault system, together with the intersection of anticline and syncline structures, produces heterogeneous stress fields that facilitate localized ruptures. Second, the seismic activity may be associated with large-scale industrial fluid injection during unconventional energy development, whereby fluids infiltrate hidden fault zones adjacent to reservoirs, altering effective fault stress conditions and triggering earthquakes. Additionally, strong earthquakes themselves can induce local stress readjustments and promote concentrated energy release.

Overall, this study provides new insights into the coupling between tectonic stress, industrial activities, and seismic processes in Changning. The findings not only contribute to a more robust assessment of regional seismic hazards but also offer important implications for understanding the potential impact of fluid injection on fault system evolution.