Vulnerability Assessment of Buildings Exposed to Deep-seated Landslide Activity in the Joshimath town of Chamoli, Uttarakhand, India

The entire Joshimath township, located in the Chamoli district of the Garhwal Himalayan region of Uttarakhand state in India, is situated on deep-seated landslides (DSLs) and is therefore prone to intermittent creep over decades. Since October 2021, accelerated surface movements localized along the DSLs have been reported. This has damaged 868 buildings and displaced nearly 1,000 people, while also damaging roads, pipelines and other infrastructure in Joshimath, and disrupting tourist revenues. Deep-seated landslides (DSLs) in high mountain regions therefore pose a significant threat to people and infrastructure and some of these landslides are capable of transforming into catastrophic failure, similar to rock avalanches. This study hence focusses on identifying and assessing the impact of DSL acceleration, on the vulnerability of buildings exposed to DSL activity in Joshimath town. For this purpose, the vulnerable areas and infrastructure are first identified based on acquired building damage data and field studies. Next the intensity of DSL activity is determined for the identified vulnerable areas/building aggregates, using satellite-based interferometric synthetic aperture radar (InSAR) techniques, which have proven to be a cost-effective method for long-term displacement monitoring over the past decades, especially in inaccessible remote regions. Therefore, this study identified vulnerable areas/building aggregates affected by accelerated DSL activity in Joshimath, and classified these exposed areas based on damage severity, resulting in an equivalent damage severity (ED) map. The equivalent cumulative displacement (ECD) was calculated for each vulnerable area under a defined damage severity level and presented as an ECD map, derived using InSAR velocities. Finally, the empirical fragility and vulnerability curves are developed for building aggregates and vulnerable areas susceptible to DSLs activity in Joshimath. These curves facilitate a quantitative assessment of potential damage and can be used as valuable tools for planning effective risk mitigation strategies for DSL activity in Joshimath town.

Keywords: deep-seated landslides (DSLs); interferometric synthetic aperture radar (InSAR); vulnerability; equivalent damage severity map (ED); equivalent cumulative displacement (ECD)