Sensitivity analysis of input ground motion on surface motion parameters in high seismic regions: A case of Bhutan Himalaya

Abstract. Historical earthquakes demonstrated that the combination of the characteristics of strong ground motion and local soil conditions significantly influence the seismic site response of a particular site. Since there are no instrumental records of past earthquakes in Bhutan, this study is the first attempt to quantify the influence of the local site conditions in the eastern fringe of the Himalaya considering various global historical earthquakes on a deterministic basis. According to the recent Global Seismic Hazard Map (GSHAP), Phuentsholing Thromde (city) in Bhutan is likely to be exposed to the peak ground acceleration (PGA) between 0.20 g–0.28 g. This particular scenario highlights the likelihood of occurrence of stronger shaking; considering the proximity of active seismic faults. To this end, we performed one-dimensional (1D) ground response analysis in eight different locations considering earthquakes with a wide variation of PGA even beyond 0.2–0.28 g so as to quantify the possible seismic response of soil strata under wide range of ground shaking. Sensitivity analysis is performed by a statistical correlation function to correlate the ground motion parameters for different earthquake shaking intensities. The amplification responses of the local soil from each input motion are projected to predict seismic hazard scenarios that highlight the ground shaking response for some locations in Phuentsholing, Bhutan, which is one of the densest urban centers in the country. The study highlights the critical range of the fundamental natural period roughly between 0.9 s to ~5.0 s with the highest range of seismic wave amplification between ~2.8 to 6.2 due to the local ground conditions, suggesting a likely aggravation during earthquakes that may lead to severe consequences especially in terms of infrastructure damages.