Preliminary assessment of seismic site effects in the fluvio-lacustrine sediments of Kathmandu valley, Nepal

Abstract

Seismic site effects are predicted adopting ground response analysis for the fluvio-lacustrine deposits of Kathmandu Valley using available geotechnical data. Equivalent linearization of nonlinear soil model has been analyzed for the study area with the geotechnical database up to the engineering bedrock level. The amplification ratio has been estimated to be varying from 1.9 to 7.8. As the peak spectral acceleration and predominant period largely contribute in the damage of structures, higher values of these parameters are consistent with the damage during 1934 Bihar–Nepal earthquake. The peak spectral acceleration for Kathmandu Valley has been estimated in a close range of 1.2725–1.2826 g. Meanwhile, the predominant period of valley soil varies from 0.27 to 0.61 s, representing the possible resonance, as 3–6 stories structures are the majority constructions in the study area. It has been contemplated that the upper 30 m of Kathmandu Valley soil would undergo large amplification with higher spectral acceleration and the predominant period shows the higher possibility of resonance with the construction trend of the buildings. Past events have shown the severity of damage level during earthquake events in Kathmandu Valley; as the capital city with the highest population density is residing in this area, similar scenario of damage may be witnessed in future events as well, so incorporating the local site effects is must. Thus, the present study provides insights on the level of risk and possible geotechnical basis for the mitigation of inherited earthquake risk in the valley.