Assessing the contemporary stress field and seismogenic structures of the Korean peninsula using focal-mechanism inversion and slip-tendency analysis

Active fault studies provide critical evidence for characterizing the tectonic stress field within the lithosphere. However, identifying and investigating such features in low-seismicity intraplate regions remains particularly challenging. In this study, we compiled focal mechanism data from the Korean Peninsula to investigate the present-day stress regime and delineate potential seismogenic zones. Using a spatio-kinematic partitioning strategy, the data were divided into four distinct structural domains. Stress inversion reveals a spatially heterogeneous regime: a transtensional strike-slip regime in the north (D4) transitioning to a dominant transpressional regime in the central and southern regions (D1–D3). The maximum compressive stress (σ₁) is predominantly horizontal and oriented ENE-WSW, shifting locally to E-W in the southeast due to the influence of subduction. By integrating regional stress tensors with sub-regional slip tendency (TsN) analysis, we evaluated the reactivation potential of focal planes, known fault geometries, and geological lineaments with hypothetical dips. This approach reveals a significant seismotectonic paradox: while mature NNE-SSW faults (e.g., the Yangsan Fault System) host the majority of documented Quaternary ruptures, they exhibit low-to-moderate slip tendency under the contemporary regional stress field. This geometric misalignment is most plausibly reconciled by depth-dependent variations in fault dip, reductions in effective normal stress via fluid overpressure, and mechanically driven localized stress deflections, all of which provide viable pathways for the reactivation of these geometrically unfavorable structures. Conversely, high reactivation potential (TsN > 0.6) is concentrated along secondary WNW-ESE and NE-SW networks, identifying them as critical yet previously underappreciated seismogenic structures that release ongoing tectonic strain. Our results indicate that this complex deformation pattern arises from the superposition of far-field stresses originating from both the India-Eurasia collision and Pacific plate subduction, further shaped by local lithospheric heterogeneities and fault-scale stress interactions.