Evaluation of ground motion parameters and seismic response of reinforced concrete buildings from the Mw 6.9, 2011 Sikkim earthquake

The continuous collision of the Eurasian plate and the Indian plate has resulted in several earthquakes in the Himalayan region. The 6.9 Mw 2011 Sikkim earthquake, which caused immense damage to the built environment in Sikkim, was triggered by an intraplate source on the overriding Eurasian plate. Strong ground motions from the earthquake were recorded at stations established by IIT Roorkee as part of the PESMOS program. In this paper, near-field and far-field ground motions from this earthquake were analyzed to evaluate their key characteristics and examine their time-frequency features by employing Fast Fourier Transforms (FFTs) and Continuous Wavelet Transforms (CWTs). A comparison between the ground motion parameters of near-field and far-field seismic waves highlights the distinct characteristics of near-field ground motions. Additionally, the impact of near-field and far-field ground motions on the seismic response of a code-compliant RC building is investigated. The results from the non-linear time history analyses indicate that the roof displacements, drift ratio and strain induced in the frame elements are less than the code-prescribed maximum limits. Further, the demand and capacity levels for the RC frame elements were evaluated to compute the performance ratios. The results indicate that the extensive damage to reinforced concrete buildings in the 2011 Sikkim quake was primarily due to the non-engineered nature of the structures and also due to the non-compliance of the built structures to the seismic design code provisions.