Abstract
The Shanxi Reservoir area is one of the most seismically active regions in Eastern China. We use the seismic waveforms, earthquake catalogs, and seismic phase observation reports to study and summarize the earthquake sequence characteristics and seismogenic background of the Shanxi Reservoir area in 2014. (1) Firstly, we relocate the earthquake sequence by the HypoDD method. The relocation results show that the dominant strike of the sequence is approximately NW-SE 129°, with a steep dip of roughly SW 84°, and the seismogenic structure contains multiple secondary surfaces (sub-faults). (2) Based on the relocation catalog, we estimate the spatial distribution of b-values along the strike of the seismogenic fault using the maximum likelihood method, and obtain the abnormal regions of stress and inhomogeneity near the fault. (3) At the same time, we also calculate the focal mechanisms for events with ML ≥ 2.5 and ML ≥ 3.0 by the HASH and CAP methods, respectively, and obtain rose statistical charts for each parameter. The results indicate that the 2014 sequence is basically of the right-lateral strike-slip type. Combined with the relocation results, we speculated that the seismogenic surface is close to the nodal plane with a strike of NW-SE 131°, a dip of SW 82°, and a rake of -173°. (4) On the basis of the focal mechanisms, we further acquire the azimuth and inclination parameters of the P and T axis for each earthquake, and get the rose statistical charts of these parameters. The P-axis and T-axis of the 2014 sequence are dominantly distributed in the NNW and SEE direction, with a gentle inclination angle, which exhibits nearly horizontal compression in the NNW direction and nearly horizontal tension in the SEE direction. (5) Finally, combined with the distribution of fault zones around the reservoir area, we infer that the 2014 sequence around the Shanxi Reservoir was the result of right-lateral strike-slip rupture of the f11 − 3 branch of the Shuangxi-Jiaoxiyang fault. We find that the 2014 sequence began to occur in areas where multiple groups of faults converge and have favorable infiltration conditions, which are regions of high-stress concentration and significant infiltration effects. The infiltration of reservoir water into deeper areas leads to an increase in pore pressure and a decrease in the strength of structural surfaces, making the rock more susceptible to rupture. Under the influence of continuous ruptures (earthquakes) and infiltration of reservoir water, the 2014 earthquakes developed along the f11 − 3 fault towards NW and SE and deeper directions.