The 28 October 2022 M_w 3.8 Goesan Earthquake Sequence in Central Korea: Stress Drop, Aftershock Triggering, and Fault Interaction

We identified the causative fault of the 2022 Goesan, Korea, earthquake sequence based on the precise relocation of the sequence that revealed a 0.8 km-long fault plane striking east-southeast-west-northwest. The fault plane encompasses the largest foreshock, the mainshock, and the majority of the aftershocks. The orientation of the fault plane is consistent with the left-lateral strike-slip motion along the east-southeast (106 degrees) striking nodal plane of the focal mechanism. The Jogok fault system recently mapped in the source area runs through the mainshock epicenter with a consistent strike and left-lateral strike-slip motion, which suggests that it is the likely causative fault of the 2022 M-w 3.8 Goesan earthquake sequence. It is a rare case of assigning a causative fault for a small-sized (M-w 3.8) earthquake with some confidence in a typical stable continental region setting, albeit no surface break observed due to deep focal depth (similar to 13 km) and the small size of the event. Aftershocks on the main fault plane, and on the adjacent subparallel fault patches seemed to be triggered by the increase in Coulomb stress caused by the mainshock. Two large aftershocks on the subparallel fault patches show slightly higher stress drops than the large foreshock and mainshock on the main fault plane, likely due to high frictional strength on those fault patches. Events of the 2022 Goesan earthquake sequence progressed rapidly in time and appear to be high stress-drop events compared with other earthquakes that occurred in other regions in Korea, probably due to the long quiescent period in the Goesan earthquake epicentral region.