The reservoir-induced 2023 Heyuan earthquake sequence in Guangdong, China and its geodynamic implications

Abstract

To better understand the mechanism of the 2023 M4.3 Heyuan earthquake sequence, we relocate the events of this sequence during January to August 2023 and determine a focal mechanism solution of the Heyuan mainshock. A total of 565 events including the mainshock are precisely relocated using the double-difference location method. Our results show that most of the events occurred in the Shijiao-Xingang-Baitian fault zone with focal depths of 7–13 km, and the aftershocks took place above the mainshock hypocenter. This sequence has obvious spatiotemporal distribution features. Before the mainshock, the seismicity was low, but within 1.5 h following the mainshock, the sequence extended toward a shallow depth and bounced back and forth in the east-west direction. Between 1.5 and 8 h after the mainshock, the sequence gradually converged to the Shijiao-Xingang-Baitian fault. After 8 h the sequence gradually extended to the eastern part of the fault. To further ascertain the seismogenic fault, we invert waveform data for the mainshock focal mechanism. Our result shows that the Heyuan earthquake had a left-lateral normal rupture with M_W 4.1 and a focal depth of 9.8 km. The strike, dip, and rake angles of nodal plane I are 334°, 64°, and − 58°, whereas those of nodal plane II are 99°, 40°, and − 137°. Among the existing faults in the study area, the strike of nodal plane I is closer to that of the Shijiao-Xingang-Baitian fault, which could be the seismogenic fault. In addition, seismic tomography revealed a high-Vp/Vs anomaly in the Heyuan earthquake area, suggesting that the Xinfengjiang Reservoir infiltration can explain why the aftershocks spread eastward. These results indicate that the 2023 Heyuan earthquake sequence is related to the seepage of the Xingfengjiang Reservoir water leading to the local crustal stress field variation, which is helpful to understand the mechanism of reservoir-induced earthquakes worldwide.