Wavelet Analysis of Near-Field Ground Motions from the Mw 7.8 2015 Gorkha Earthquake

Abstract

AbstractThe 2015 Nepal earthquake was one of the strongest quakes to strike the landlocked Himalayan country. The earthquake resulted in strong ground motions that severely affected various structures in the region. The unreinforced masonry structures were destroyed. Recorded ground motions from only five stations are available in the public domain. However, characterizing these ground motions in the time domain does not provide any information about the sequence of frequencies and amplitudes arriving at the station, which are key to understanding structural damage. The continuous wavelet transforms (CWT) are useful for such improved characterization of ground motions, as they provide a 3D view of time, frequency, and amplitude, thus enabling a comprehensive understanding of the damage potential of the ground motions. In this paper, recorded near-field ground motions from the earthquake are analyzed in the time and frequency domains. It is observed that the response spectra show a very wide acceleration sensitive region and some ground motions contain significant velocity pulses, both of which strongly influence structural damage. Further, it is observed that CWTs properly represent the critical characteristics of ground motions which can be correlated with the observed non-uniform damage to the built environment.KeywordsStrong ground motionsFrequency contentFast fourier transformsContinuous wavelet transformsTime–Frequency analysis2015 Nepal earthquake