A hybrid approach to earthquake-preconditioned debris flow: regional susceptibility and event-based hazard assessments

Abstract The Tut region of Adıyaman in southeastern Türkiye experienced destructive debris flow events on 15 March 2023, following a period of intense rainfall under post-seismic conditions. These flows were spatially and temporally associated with the destabilizing effects of the Kahramanmaraş earthquake sequence, which had earlier weakened slope materials generating extensive coseismic landslide debris and initiating destructive debris flows in a region where these processes had not previously been documented. Subsequent high-intensity precipitation rapidly mobilized saturated colluvial materials along steep terrain, causing severe socio-economic damage and two confirmed fatalities. Field observations and remote sensing analysis revealed that 396 debris flows were initiated on slopes composed predominantly of weathered marl, shale, and clayey limestone lithologies that are particularly susceptible to failure under elevated pore water pressure conditions. Initially, a susceptibility analysis was conducted using a machine learning-based logistic regression model, incorporating relevant independent variables primarily derived from digital elevation models. The model achieved high predictive performance, with an area under the receiver operating characteristic curve of 0.90. To complement susceptibility mapping and capture initiation and propagation of debris flow dynamics, physically based numerical simulations were conducted using the RAMMS model, calibrated through back-analyses of three catastrophic debris flow events. Back-analyses of the events provided estimates of flow intensity parameters, showing strong agreement with observed characteristics, thereby validating its application in cascading earthquake-rainfall hazard assessments. This study presents the first integrated debris flow susceptibility and numerical modelling framework by combining data-driven and physics-based approaches, it advances understanding of cascading earthquake-rainfall hazards and provides a robust foundation for debris flow hazard assessment. The generated susceptibility and hazard maps are expected to enhance awareness, preparedness, and planning efforts among local communities, engineers, and land-use decision-makers.