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

254 PATA Days 2024 the CW. A third earthquake event is indicated by fissures cutting through the gravel layer covering the fissure-filling sediments, and a fourth event by the cutting of overlying sand and clay layers. Subsequently, a horizontal clay layer that cuts across these layers suggests a possibility of up to five earthquake events in this trench. Previous studies reported at least three earthquake events in the northern extension of Trench_B (Lee et al., 2015; Song et al., 2020). However, this study site indicates two additional seismic activities, which could suggest that the trench fromprevious studies was either in a different segment, or the absence of sedimentary layers or erosion might have led to the loss of earthquake evidence. However, given the close proximity of the excavation locations, their placement on the same lineament, and the absence of any segment boundary features such as bending, stepping, branching, or gaps between the previous and current trenches, the latter scenario is considered more likely. Currently, samples for OSL, radiocarbon, and cosmogenic dating have been collected from trench_B for chronological analysis. If supported by dating results, this could provide significant information regarding the timing and recurrence intervals of earthquakes. Lateral slip rate and surface deformation mechanism Geomorphic offset and dating allow for the derivation of long-term slip rates. In this study, geomorphic offset markers (terrace risers) have revealed an accumulated displacement of approximately 20-30 meters. The classification of terrace surfaces was conducted based on elevation and slope, and the cumulative horizontal displacement rate will be calculated using the results of dating obtained from trenches and pits excavated at representative locations of each geomorphic surface. A C K N O W L E D G E M E N T S This research was supported by a grant (2022-MOIS62- 001(RS-2022-ND640011)) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety (MOIS, Korea). R E F E R E N C E S Cheon, Y., Choi, J.-H., Choi, Y., Bae H., Han, K.-H., Son, M., Choi, S.-J., & Ryoo, C.-R. (2020). Understanding the distribution and internal structure of the main core of the Yangsan Fault Zone: Current trends and future work. Journal of the Geological Society of Korea 56 , 619- 640 (in Korean with English abstract). Cheon, Y., Ha, S., Lee S., Cho, H., & Son, M. (2017). Deformation features and history of the Yangsan Fault Zone in the Eonyang-Gyeongju area, SE Korea. Journal of the Geological Society of Korea 53, 95-114 (in Korean with English abstract). Choi, J.-H., et al. (2021). Research in active tectonics and development of fault segment model for intraplate regions (R&D Report GP2020–014). KIGAM, Daejeon, 140 p. Ko, K., Choi, S.-J., Lee, T.-H., Gihm, Y.S., Kim, C.-M., Kim K., & Cheon, Y. (2022). A multidisciplinary approach to characterization of the mature northern Yangsan fault in Korea and its active faulting. Marine Geophysical Research 43, 21. https: // doi.org/10.1007/s11001-022-09486-w Lee, J., Rezaei, S., Hong, Y., Choi, J.-H., Choi, J.-H., Choi, W.-H., Rhee, K.-W., & Kim, Y.-S. (2015). Quaternary fault analysis through a trench investigation on the northern extension of the Yangsan fault at Dangu-ri, Gyungjusi, Gyeongsanbuk- do. Journal of the Geological Society of Korea 51, 471 - 485 (in Korean with English abstract). Song, Y., Ha, S., Lee, S., Kang, H.-C., Choi, J.-H., & Son, M. (2020). Quaternary structural characteristics and paleoseismic interpretation of the Yangsan Fault at Dangu- ri, Gyeongju-si, SE Korea, through trench survey. Journal of the Geological Society of Korea 56, 155 - 173 (in Korean with English abstract).