Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

56 PATA Days 2024 GEOMORPHIC ANALYSIS Previously available geological maps at a 1:50,000 scale, along with vintage aerial photos and high- resolution LiDAR DEM (0.5 m resolution), were used for detailed active fault mapping and identifying tectonic geomorphic markers. The first detailed lineament mapping was carried out using the high-resolution DEM created from LiDAR DEM. The lineaments were classified into first grade and second grade based on their length. Our detailed lineament analysis suggests that NE-SW trending lineaments slightly differ from previously reported YF (Fig 2b). Field validation of the lineaments mapped from LiDAR DEM revealed several meter-scale fault cores showing reactivation from left-lateral to right-lateral fault movement along these NE-SW trending lineaments. It indicated that the YF undergo complex fault evolution histories. Detailed field interpretation of the fault outcrops observed here, combined with the current tectonic stress field of the Korean Peninsula, suggests that the kinematics of the YF is suitable for transpressional strike-slip faulting. Using LiDAR DEM and aerial photos, we identified several tectonic landforms such as back tilting of the hill face, triangular facets, truncated streams, and linear valleys/ depressions along the YF. At the Mangye-ri site along the YF, several channels show right-lateral offsets (Fig. 3). Detailed mapping using LiDAR DEM identified three channels with right-lateral offsets of 39.4 m, 55.2 m, and 56.3 m, respectively. To calculate the amount of offset, we defined the best-fitted line based on up=streams and the piercing point that deviates from this line (Lee et al., 2019). We interpret this evidence as indicative of neotectonic activities along the YF, highlighting the need for detailed paleoseismic studies. INTERPRETATION OF GEOPHYSICAL SURVEY To pinpoint the exact fault trace location and find a suitable trench site, we conducted an Electrical Resistivity Tomography (ERT) survey at several locations along the YF. Out of these, 2 ERT profiles revealed geophysical anomalies consistent with our previous field and geomorphic analysis results. The trench site was determined to be between these two ERT profiles, which clearly indicated fault-related anomalies (Fig. 3). Profile 1, a 130-m-long profile with 5-meter spacing, is located 100 meters (Fig. 3c). It exhibited resistivity values ranging from 100-3000 Ω·m. Profile 1 shows a couple of high-resistivity layers ranging from 30-70 m (HR 1) and 80-130 m (HR 2), respectively. A low- resistivity layer (LR 1), overlain by HR 1, initiates at 85 m and slightly thickens to a depth of ~10 m at 35 m. We interpret the bedrock to correspond to the high- resistivity layers, and HR 1 reaching the surface aligns well with the location of a knickpoint. Additionally, the relatively low-resistivity zone between HR 1 and HR 2 represents the fault zone. Profile 2, an 84-1499 Ω·m range profile that is 100 meters long with 5-meter spacing. It shows a clear low-resistivity zone (LR 2) between high-resistivity layers (HR3 andHR4). Due to the resistivity values (< 150 Ω·m), the location of the knickpoint, and the similarity to profile 1, LR 2 indicates a wide fault core zone. A low-resistivity layer (LR 3), approximately 5 meters thick, is identified above HR