The role of fluid migration along strike-slip faults in triggering the 2021 Mw 5.0 Yancheng earthquake in the South Yellow Sea, East Asia

The South Yellow Sea (SYS) has experienced many moderate-strong earthquakes in the last four decades. On 17 November 2021, an Mw5.0 earthquake with a dextral strike-slip mechanism occurred in the Yancheng area of the SYS, resulting in various degrees of ground motions in many coastal cities of eastern China, such as Shanghai and Nanjing. The epicenter of the Yancheng event was characterized by the prevalent emplacement of hydrothermal vent complexes and strike-slip faults. However, the relationship between the strike-slip fault, the associated fluid migration and the Yancheng earthquake is poorly understood. Based on multichannel seismic profiles and well data acquired over the last 10 years, this study conducted a comprehensive investigation of the seismogenic strike-slip fault of the Yancheng event. Subsequently, the role of fluid migration along strike-slip faults in triggering this earthquake was analyzed. The result suggested that the active faults in the SYS were characterized by a conjugate fault system, the NNE trending strike-slip faults and the NW trending strike-slip faults. The NNE-trending fault F1 passing through the epicenter of this event is suggested as the seismogenic fault. The fault F1 and other active faults in the SYS were probably inherited from the pre-existing strike-slip faults formed during the late Jurassic to early Cretaceous. Various hydrothermal vent complexes were identified near the fault F1. Seismic facies analysis suggested that the hydrothermal activities could have continued to the Miocene and Quaternary in the vicinity of the fault F1, almost simultaneous with the reactivation of the fault F1 and other active strike-slip faults. The reactivation of the pre-existing faults and the associated hydrothermal events were suggested to be caused by the subduction of the Pacific Plate. We proposed that the hydrothermal fluid may have migrated along the F1, which further enhanced the faults’ slip, and finally triggered the Yancheng Mw 5.0 earthquake and other historical events in the SYS.