Quantifying the Contribution of Tectonic Stress to Landslide Development in the Xianshuihe Fault Area, Southeastern Tibetan Plateau

Tectonic stress is a critical factor influencing landslide development; however, quantitative studies on its mechanical effects remain limited. The Xianshuihe Fault area in the southeastern Tibetan Plateau exhibits significant dynamic movements, complex topography, and frequent earthquake-induced landslides. In this study, tectonic and topographic stress were calculated for 16 zones–eight near faults and eight farther away. A systematic analysis was conducted on the relationships between tectonic and topographic stress magnitudes in accordance with the characteristics of the existing landslides (e.g., slope azimuth, length, and angle). The results indicate that the landslide movement azimuths in near-fault zones generally align with the fault dip and deviate slightly (within approximately 30°) towards the orientation of the maximum horizontal principal stress (S_H). Landslides in most near-fault and far-fault zones show azimuths within 0°–45° towards the S_H orientation, suggesting the influence of the tectonic stress field. The magnitude of tectonic stress portion (P_Tect) suggests that tectonic stress is approximately 40–90% of the initial stress magnitudes. Specifically, P_Tect values in near-fault zones show the range of 60–90%, while those in far-fault zones are 10–30% lower, falling within the range of 40–80%. Our findings suggest that tectonic stress initially balances counteracting topographic stress. The reduction of tectonic stress due to external factors decreases P_Tect from 80–90% to 40–60%, disturbing the balanced stress state and likely causing landslides. Our results quantitatively demonstrate the role of tectonic stress in landslide development.