Intraplate Repeating Earthquakes in the Rupture Area of the 2008 Gyeryongsan, Korea, Mw 3.6 Earthquake

Summary Repeating earthquakes are believed to result from recurring ruptures of a single asperity, driven by surrounding aseismic creep. However, their occurrence and behavior in intraplate regions remain poorly understood. This study investigates the repeating earthquakes in the Gyeryongsan region of the Korean Peninsula, a tectonically stable intraplate region, following the 2008 Mw 3.56 earthquake. We augmented the earthquake catalogue from 2007 to 2022 using template matching and identified one repeating earthquake family comprising ten events with irregular recurrence intervals. The repeating earthquakes, with a median magnitude of Mw 1.22, occurred within the rupture area of the Mw 3.56 mainshock, beginning in late 2010 and subsequently recurring intermittently between 2011 and 2019. Stress drops of nearby earthquakes increased gradually from 0.3-0.9 MPa to 8.6 MPa over a decade, indicating a fault strength recovery period substantially longer than that typically observed at plate boundaries. We interpret that the earthquakes occurred within a damaged fault zone, reflecting extremely low loading rates in the intraplate region. Our study provides insights into earthquake behaviour within intraplate damaged fault zones and documents a rare case of a repeating earthquake family that persisted over ∼12 years.