Probabilistic Seismic Hazard Analysis (PSHA) to estimate the input ground motions for Co-seismic landslide hazard assessment: A case study on Himalayan highways, Sikkim India

Abstract

Sikkim, the North-Eastern state of India, along with its neighbouring region is recognized as a part of the ‘Alpine-Himalayan global seismic belt’, which is one of the most seismically active areas of the world. Four significant earthquakes with a magnitude higher than Mw = 8.0 were reported in this area in earlier years of 1897, 1905, 1934, and 1950. The 2011 (Mw = 6.9) Sikkim and 2015 (Mw = 7.8) Gorkha Nepal earthquakes call attention to the need for a more accurate understanding of seismic characteristics in the Sikkim and their nearby region to minimize loss of life and properties due to future earthquakes and related co-seismic hazards. This study aims to estimate the Peak Ground Acceleration (PGA) having a known Probability of Exceedance (PoE) along Gangtok to Lachung and Gangtok to Tsomgo Lake; two strategic highways within Sikkim. The PGA with a known PoE is an essential input required for earthquake-triggered landslide susceptibility analysis on a regional scale as well as for the dynamic slope stability assessment of the prevailing hill slopes along the highways corridor in Sikkim. Therefore, a Probabilistic Seismic Hazard Analysis (PSHA) of the highway corridors in Sikkim is presented utilizing the updated earthquake catalogue, modified seismic sources, and next-generation attenuation relationships. The Uniform Hazard Spectra (UHS) and total hazard curves corresponding to the bedrock site conditions are generated employing ‘EZ-FRISK’ software. The variations of PGA having a 10% PoE in 50-years along the highways are estimated to identify the critical sections based on the ground acceleration parameter.