Regional Characteristics of Seismicity Associated with Hydraulic Fracturing in the Southern Sichuan Basin of China

In the southern Sichuan Basin of China (SSBC), hydraulic fracturing (HF) production of shale gas and surface buildings have been seriously affected by some medium scale (local magnitude ML > 4.0) earthquake events. In this study, focusing on relocated hypocenters in SSBC from January 2016 to May 2017, the Density-Based Spatial Clustering of Applications with Noise algorithm was introduced to divide it into four seismic regions. The temporal evolution of seismicity parameters, detailed views of potential faults near injection wells and spatial migration of seismic activity in each region were obtained. Moreover, the statistical correlation between seismicity and engineering disturbance was calculated by adopting epidemic type aftershock sequence model (ETAS); the relationship between corner frequency, stress drop and seismic moment of each region were analyzed, and the spatial distribution of the stress drop, the relationship with the focal mechanism solutions (ML > 3.5) and the fault slip-tendency under the regional stress pattern were discussed. The results show that the seismic diffusion rate of each region can be well described by the square root envelope (0.3–0.8 m2/s) and seismicity has a strong cluster mode (triggered events) and a weak background mode (independent events). Most (more than 97.5