## 1 Introduction
### Regional Seismotectonic Context of the Korean Peninsula  
These microstructural and geochemical characteristics underscore the potential for episodic fault reactivation under varying stress conditions. Notably, recent studies on intraplate deformation in stable continental interiors--such as northwestern Iberia [19], southeastern France [20], and central Australia [21]--demonstrate that inherited fault structures, lithological contrasts, and far-field stress transmission can drive localized deformation even in tectonically quiescent settings. These findings challenge the conventional view of continental interiors as mechanically dormant and highlight the importance of characterizing stress accumulation and strain localization mechanisms in such regions.  
Although such intraplate settings are often underestimated in terms of seismic hazard, the Korean Peninsula exhibits similar geological traits, such as inherited fault systems and heterogeneous crustal composition.  
In this context, the Korean Peninsula, often classified as a stable intraplate region, may still harbor structurally inherited faults capable of storing and releasing tectonic stress over geologic timescales. Therefore, comprehensive investigations that integrate geodetic strain measurements, microstructural analysis, and regional geomechanical modeling are essential to accurately assess long-term seismic potential and develop effective earthquake preparedness strategies.  
This geomechanical evidence is further substantiated by historical records, which provide direct observations of past seismic activity along the fault.  
Historical earthquake records further corroborate the seismogenic potential of the Yangsan Fault. The Annals of the Joseon Dynasty report a significant seismic event in 1643 CE (region of [PERSON]), during which surface rupturing and groundwater upwelling were observed in the Ulsan region, accompanied by a tsunami. Another major earthquake was documented in 1681 CE (region of [PERSON]), and both events are estimated to have exceeded a moment magnitude (Mw) of 6.5. Based on such historical accounts, some researchers have proposed a recurrence interval of approximately 400 years for large-magnitude earthquakes along the fault. However, this hypothesis remains tentative and has not yet been established as a consensus within the geoscientific community.  
Geophysical data provide further insight into the fault's segmentation and crustal environment. Ref. [22] used gravity field interpretation to detect significant variations in density and structural depth along the fault, particularly in the central segment, indicative of complex interactions with surrounding tectonic features such as the Yeonil Tectonic Line. These structural discontinuities may act as barriers or triggers for rupture propagation, influencing earthquake magnitudes and rupture extents.  
Although the Korean Peninsula lies within a tectonically stable intraplate setting, recent moderate earthquakes--such as the 2016 Mw 5.8 Gyeongju and 2017 Mw 5.4-5.5 Pohang events--demonstrate active faulting in southeastern Korea. This region, which hosts most of the nation's nuclear power infrastructure, requires high-resolution deformation monitoring and seismic hazard assessment to ensure disaster preparedness and structural resilience.  
To this end, high-resolution geomorphic and structural mapping techniques have been increasingly employed to delineate active fault systems with greater precision. In particular, LiDAR-based analyses have proven effective for identifying fault scarps and subtle geometric offsets in Korea. For instance, ref. [23] utilized high-resolution digital elevation models (DEMs) to map surface features along the central Yangsan Fault, which were subsequently integrated with trenching and geochronological data by [24] to construct segment-based rupture scenarios for regional seismic hazard modeling.