Seismically induced Landslide hazard assessment based on the spatial distribution of the slope strength demand in the Western Himalayas

Earthquake-induced landslides are among the most common seismic hazards in Indian Himalayan high terrains, claiming hundreds of lives and infrastructural losses. Uttarakhand state is in the Western Himalayas and comes under high seismic activity zones as per the seismic code of India. However, a detailed seismically induced landslide hazard assessment is unavailable for the region. Therefore, a parametric time probabilistic approach was used to evaluate the co-seismic landslide hazard in Uttarakhand. Characteristics of the seismicity affecting the area were considered to estimate the critical acceleration (A_c)_x(p,t) that slopes should have to limit the probability of exceedance of Newmark displacement value x within time t. Initially, occurrence probabilities for different degrees of seismic shaking for a time frame of 50 years were calculated in terms of Arias intensity. Then, the spatial distribution of the slope strength demand was mapped using the empirical relationship of the Newmark displacement with Arias intensity and critical acceleration. Newmark displacement of 2 and 10 cm were considered critical thresholds with a 10% probability of exceedance. The obtained results suggested that the significant part of the region along the Main Boundary Thrust (MBT) and Main Central thrust (MCT) have Arias Intensity value greater than 2 m/s. Higher Arias intensity values of approximately 4.5 m/s for soil slope conditions and 3 m/s for rock slope conditions were observed throughout the lesser Himalayan zone. In these areas, for the thresholds mentioned above, the exceedance probability in 50 years reaches 50% in the case of 0.32 m/s for soil slope conditions and 70% in the case of 0:11 m/s for rock slope conditions. By comparing the anticipated strength demand with the actual critical acceleration values computed from slope material parameters and slope angle, the resultant slope strength demand maps could offer the basis for determining if particular slopes have a considerable failure probability.