Quaternary surface ruptures of the inherited mature Yangsan fault: implications for intraplate earthquakes in Southeastern Korea

Abstract. Earthquake prediction in intraplate regions, such as South Korea, is challenging due to the complexity of fault zones. This study employed diverse methods and data sources to detect Quaternary surface rupturing along the Yangsan Fault to improve seismic hazard assessment. Paleoseismic data were analyzed to reveal insights into seismic activity, displacement, and structural patterns. Observations from five trench sites indicate at least three faulting events during the Quaternary, with the most recent surface rupturing occurring approximately 3,000 years ago. These events resulted in a cumulative displacement of 3.1–94.0 m and maximum estimated magnitude of 6.7–7.2. The average slip rate of 0.14 mm/yr suggests a quasi-periodic model with possible recurrence intervals exceeding 10,000 years. The structural patterns imply the reactivation of a pre-existing fault core with top-to-the west geometry, causing a dextral strike-slip with a minor reverse component. This study underscores the continuous faulting along the inherited mature fault, the Yangsan Fault, since at least the Early Pleistocene, contributing valuable insights for seismic hazard assessment in the region and offering a broader understanding of intraplate earthquake dynamics for earthquake prediction.