Emergency Investigation and Failure Mechanism Analysis of the 2025 Junlian Landslide Based on Interferometric Synthetic Aperture Radar and Terrestrial Laser Scanning

Rapid acquisition of critical failure characteristics following a landslide is essential for effective emergency response and risk mitigation. However, in complex terrain, conventional field investigations are often restricted by inaccessibility, adverse weather conditions, and potential safety hazards. These constraints impede the rapid and comprehensive disaster assessment, thereby compromising the efficiency of emergency decision-making. Taking the 2025 Junlian landslide in Sichuan, China, as a case study, this study combines time-series interferometric synthetic aperture radar (InSAR) and terrestrial laser scanning (TLS) to establish a rapid, non-contact framework for landslide emergency investigation and failure mechanism analysis. Deformation evolution was reconstructed via time-series InSAR analysis combined with transfer entropy (TE) causality detection, facilitating the extraction of characteristic deformation patterns. Concurrently, high-resolution three-dimensional (3D) terrain models were generated utilizing TLS and unmanned aerial vehicle (UAV) data. This allowed for the automatic identification of discontinuities to reveal their spatial distribution and elucidate their control over the failure mechanism. The investigation identified four dominant joint sets. Two conjugate joint sets dissect the rock mass into wedge-shaped blocks, constituting the structural prerequisite for wedge toppling failure. Extreme rainfall in early 2025 significantly degraded the shear strength of discontinuities and weak interlayers, ultimately triggering slope failure. The results demonstrate that the proposed framework overcomes the limitations of traditional methods in timeliness and safety, providing an efficient, precise, and non-contact solution for post-landslide emergency investigation and mechanism analysis.