169-8 Quaternary Faulting in a Low-Seismicity Region: A Case Study from the Yeongdong Fault, Korea

Session: Advances and Challenges in Seismotectonic Studies in Slow-Deforming Regions

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Abstract:

 The 2016 Gyeongju earthquake (Mw 5.8) and the 2017 Pohang earthquake (Mw 5.4) highlighted the importance of earthquakes and seismic hazard to the Korean public, even far from plate boundaries. Thus, the Korean government launched the Active Fault Mapping Project of the Korean Peninsula in 2017. The first stage was focused on the seismically active southeastern region, and the second stage has been ongoing in the capital area since 2022. This study presents an example of the paleoseismological investigation conducted along a relatively low-activity fault system in the second-stage area.

 In the second-stage region, major faults such as the Yeongdong, Gongju, and Chugaryeong faults generally trend NE–SW to NNE–SSW and are considered to have originated as strike-slip faults during or before the Cretaceous. This study focuses on one of the faults, the Yeongdong Fault, where some evidences of Quaternary faulting were identified.

 First of all, a detailed geomorphic analysis was conducted using LiDAR imagery and historical aerial photographs in the southwestern part of the Yeongdong Fault. The analysis revealed two beheaded streams and three deflected streams along a lineament, suggesting right-lateral displacement. Electrical Resistivity Tomography (ERT) surveys identified the low-resistivity anomaly zone, guiding the selection of trench sites. Trenching revealed a fault cutting through Quaternary deposits. The slickenline observed on the fault plane (~20ºN rake) indicates right-lateral strike-slip motion, which is consistent with the horizontal displacement inferred from geomorphic features. Two faulting events are identified on the trench exposure. Associated with the most recent event, an apparent vertical displacement of approximately 0.87 m is observed. Based on the rake of the slickenline, the amount of net slip was estimated to be about 1.62 m. Applying this value to an empirical relationship between maximum displacement and moment magnitude yields a moment magnitude (Mw) of approximately 6.9. The OSL age obtained from the offset sediment is approximately 11 ka, indicating that the event likely occurred during the Holocene.

 Although much remains to be understood—such as the segmentation of fault systems, segment-specific slip rates, and recurrence intervals—the challenges in characterizing these aspects remain substantial. However, continued research in the future is expected to improve our understanding of these elements and ultimately contribute to a more accurate assessment of the potential seismic hazard associated with these fault zones.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8629

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