Co-seismic Landslide Susceptibility Assessment Using a Modified Newmark Model: A Case Study of the 2016 Mw 6.7 Imphal Earthquake

The North Eastern Region (NER) of India is one of the most seismically active zones, where earthquake-induced landslides pose a major threat to the settlements, infrastructure, and livelihoods. Objectives: The objectives of this research are to assess the co-seismic landslide susceptibility in the Imphal area of Manipur, Northeast India, by incorporating the effect of earthquake-induced ground motion into the slope stability analysis using the modified Newmark Sliding Block Model. Background: The critical gap in landslide susceptibility research in the Imphal region of NER is the lack of earthquake triggering in physically based slope stability modelling. Methods: The Peak Ground Acceleration (PGA) data for the Mw 6.7 Imphal earthquake (January 4, 2016) were collected from the USGS database and converted to Peak Horizontal Acceleration (PHA) at the ground surface using the non-linear site response relationship for National Earthquake Hazards Reduction Program (NEHRP) site class D conditions. A Deterministic Seismic Hazard Approach (DSHA) was considered to simulate the scenario-based ground motion input to the slope stability analysis model. The critical factor of safety (FSc) was computed by integrating the effect of seismic acceleration and terrain parameters, particularly slope gradient, into the slope stability analysis using the modified Newmark model. Findings: This study highlights a scenario-based co-seismic landslide vulnerability; the M 6.7 Imphal earthquake shows PGA ranging from 0.1 to 0.24 g with highest intensities near the epicenter, and ~ 70.2% of the area is moderately susceptible, 18.3% low, and 11.5% highly susceptible, showcasing priority areas for hazard mitigation during future M ≥6.7 earthquake events. Novelty: The novelty of this research is that it uses a physically based co-seismic landslide susceptibility analysis that incorporates the role of seismic forces in the analysis of slope instability, as opposed to the conventional approaches that are based on the terrain parameters alone. Keywords: Co-seismic, Landslide Susceptibility, Modified Newmark Model, Earthquake, Imphal