Abstract

We analyze ground motions produced by the 25 April 2015 Gorkha, Nepal, earthquake (Mw 7.9) and five of its larger aftershocks (5.3Mw7.2) which were recorded in the distance range 100–900 km by two recently installed strong‐motion networks in the Indo‐Gangetic Plains (IGP). In comparison with the largest Mw 7.2 aftershock, we find that the peak ground accelerations (PGAs) of the Mw 7.9 mainshock are somewhat higher, but peak ground velocities (PGVs) and peak ground displacements (PGDs), respectively, are roughly equal or even smaller. Furthermore, PGAs of the 26 April Mw 6.7 aftershock are similar to those of the Mw 7.2 aftershock, but PGVs and PGDs are much smaller. PGAs in the IGP during the sequence are associated with frequencies f of 4  Hz, whereas PGVs and PGDs occur at f0.1  Hz. This implies that the source spectrum of the Mw 7.9 mainshock at f0.1  Hz was similar to that of the Mw 7.2 aftershock, whereas the spectral levels of the Mw 7.2 and 6.7 aftershocks were nearly equal at f4  Hz. This is confirmed by spectral ratios at the IGP sites: the ratios of the Mw 7.9 mainshock to the Mw 7.2 aftershock are about 1 in the intermediate frequency range of 0.04–0.3 Hz, whereas those of the Mw 7.2–6.7 aftershocks are 1 at f>1  Hz and 10 at f0.1  Hz. This is also in agreement with reported teleseismic moment‐rate spectra of these three events. Existing ground‐motion prediction equations (GMPEs), based on worldwide data, do very poorly in predicting observed peak motions during the Gorkha sequence. Hence, we develop a new GMPE for the region which, in spite of the sparse dataset and peculiarities of some of the events, should provide a more reliable estimation of seismic intensities than those presently available.

You do not currently have access to this article.