Unravelling a midcrustal seismogenic fault structure from a seismic sequence and geophysical data: application to the 28 October 2022 M L 4.1 Goesan earthquake in the central Korean Peninsula

Earthquakes in the Korean Peninsula often occur in subsurface hidden faults that are hardly identified before the seismic activity. We investigate a midcrustal subsurface hidden fault in a seismically quiescent region of the central Korean Peninsula that produced the 28 October 2022 ML 4.1 earthquake. A combined analysis of seismicity, geophysical properties and geological features constrain the subsurface fault geometry. The midcrustal fault may extend to the lineament on the surface that presents low gravity anomalies. The focal mechanism solutions and seismicity distribution suggest that the lineament may correspond to the surface trace of the fault. Further, the responsible fault is a left-lateral strike-slip fault with dip of 88° and bilateral rupture at depths of ∼12–14 km. The lateral extent of the fault may reach >25 km. A series of foreshocks formed the source zone to induce the main shock. The main shock nucleated at a location of lateral contrasts of heat fluxes and magnetic anomalies in the fault. The strong ground motions by the main shock are amplified by the sedimentary layers in the event site, inducing aftershocks to spread along the fault with time. The fault orientation is laid to respond to the ambient stress field. The Coulomb stress changes induced by the main shock load stress the fault, increasing the possibility of another earthquake occurrence. The study suggests that a combined analysis of seismicity, geophysical properties and geological features may provide constraints on seismogenic subsurface hidden faults.