The 4 January 2020 offshore Pearl River Estuary earthquake sequence in South China: Implications for seismic potential of the NW-striking local faults

•We determine hypocentral parameters of the 2020 Pearl River Estuary (PRE) earthquake (M3.5) and its aftershocks, as well as their focal mechanisms.•The 2020 PRE earthquake sequence was mainly caused by rupture of the NW-striking Qi’Ao-Guishan fault in the PRE.•Both the NW- and NE-striking faults in the PRE have seismogenic potential in the GHMGB, and even in the whole coastal area of the northern SCS, which should be paid much attention. The complexity of intraplate earthquakes and their challenge to current earthquake models persist as an important scientific and social problem, both about their causes and the resulting hazards. The Guangdong-Hong Kong-Macao Greater Bay area (GHMGB) is located in the coastal seismic zone of South China. Due to the huge residential population and important economic status, seismic hazard in the GHMGB often causes widespread concern. In this work, waveform data of the 2020 Pearl River Estuary (PRE) earthquake (ML3.5) and its aftershocks are carefully analyzed using about 6-month data recorded at 124 local seismic stations. A total of 8 aftershocks are identified.We determine the hypocentral parameters of the PRE mainshock and its aftershocks, as well as their focal mechanisms.Our results show that the 2020 PRE earthquake sequence is distributed in a NW-SE direction with a lateral extent of about 3.5 km, which is consistent with the location of the NW-striking Qi'Ao-Guishan fault. The 2020 PRE earthquake and its aftershocks exhibit similar focal mechanisms. According to the stereographic projection results of the P and T axes, the orientation of the principal compressive stress is oblique to the NW-striking Qi'Ao-Guishan fault, hence these earthquakes are mainly characterized by left-lateral strike-slip faulting. In combination with many previous geological and geophysical results, we suggest that the NW-striking faults could have similar seismogenic importance as the NE-striking faults in the GHMGB and even the whole coast of the northern South China Sea, especially at the intersection of the NW- and NE-trending faults.