Deciphering the force history of 2021 Chamoli rockslide

Landslides are a significant hazard, particularly for those living in mountainous regions where the terrain is steep and unstable. Unfortunately, continuous monitoring of landslides is challenging due to their unpredictable nature. However, recent advancements in high-quality, dense broadband seismic networks have made it possible to study the spatial and temporal evolution of mass wasting processes through the analysis of seismic signals. The 2021 Chamoli rockslide which originated from a glaciated ridge of the Ronti Mountain in the western Himalaya caused severe damage to a hydropower project in downslope region and a casualty of about 80 people. CSIR-National Geophysical Research Institute established a regional seismic network in the Uttarakhand Himalaya which provides a great scope to understand this event in greater detail. We have performed dynamic inversion of the long period seismic waves generated by the rockslide to derive its force history. We used multistation data from Uttarakhand regional seismic network. We used IRIS syngine to generate Green’s function based on ak135 velocity model. Long period seismic waveforms from 6 stations within a distance of 80 km were chosen to perform inversion based on the signal to noise ratio and azimuthal coverage. The inversion is done using python package called lsforce. We reconstruct the force time history of the landslide, from the initial detachment of the rock mass to its impact on the ground. The peak upward vertical force corresponds to the detachment and peak downward vertical force corresponds its  the imapct  onto the ground. The result agrees with the centroid single force inversion done for the phases of detachment and impact of the landslide. The result obtained from force time history can be used to constrain parameters for the numerical simulation of the landslide to understand its dynamics in detail.