Abstract: Fluid injection-induced seismicity has garnered global attention, causing a key technical challenge to the safe extraction of clean energy resources, such as shale gas. Taking a representative shale gas development area in the southern Sichuan Basin as the background, this study investigated the evolution and fluctuation of seismicity parameters during fluid injection, and examined the spatiotemporal dynamics of the seismic front and back-front behavior. The underlying fluid-driven patterns of earthquake swarms in the region were explored. The results show a clear spatiotemporal correlation between fluid injection and moderate-to-strong earthquakes (M_L ≥ 3.5), with the injection process significantly enhancing the intensity and complexity of seismicity. We confirm the ubiquity of the seismic back-front phenomenon, characterized by a progressively expanding central zone devoid of seismicity. The seismic front and back-front are found to be controlled by aseismic slip, while the swarms between them are governed by a combination of mechanisms: alternating dominance of slow diffusion driven by fluid pressure and rapid migration driven by aseismic slip. These findings helps the understanding of the physical origins of fluid-induced seismicity in shale gas regions, as well as for assessing and mitigating associated seismic hazards.