Comprehensive Analysis of Late Quaternary Faulting and Earthquake Potential on the Cheongun-Dong Fault, Southeast Korea: Implications for Intraplate Seismic Hazards in a Slow Tectonic Regime

Intraplate tectonic settings, characterized by dispersed and poorly defined small faults, challenge seismic hazard assessment due to their subtle surface expression and low slip rates, yet they can generate infrequent but damaging earthquakes by accumulating strain over time. Recent paleoseismic studies along Korean peninsula have challenged the long-standing perception of the Korean Peninsula—an intraplate region—as seismically stable. However, research has largely focused on major faults like Yangsan and Ulsan, with limited attention given to smaller, potentially seismogenic faults between these two faults. This study addresses that gap by presenting the first paleoseismic investigation of the Cheongun-dong fault (CDF), an ∼6–7 km long dextral strike-slip fault near Gyeongju city—an area historically impacted by strong earthquakes. Trenching and stratigraphic analyses reveal evidence of four surface-rupturing paleoearthquakes within the past ∼68,000 yr, with recurrence intervals ranging from 6,500 to 12,000 yr. The most recent event occurred around 37 ka, and the earliest dates back to before 54 ± 2 ka. The CDF exhibits a slip rate between 0.02 and 0.17 mm/yr in Late Pleistocene and is capable of generating earthquakes exceeding Mw 6.5. These findings underscore the critical role of small-scale faults in intraplate seismicity and emphasize the importance of incorporating such faults into regional seismic hazard models to improve long-term risk evaluation in Korea and other areas of similar tectonic setting.