Variable anelastic attenuation and site effect in estimating source parameters of various major earthquakes including Mw 7.8 Nepal and Mw 7.5 Hindu kush earthquake by using far-field strong-motion data

Strong-motion records of recent Gorkha Nepal earthquake (M-w 7.8), its strong aftershocks and seismic events of Hindu kush region have been analysed for estimation of source parameters. The M-w 7.8 Gorkha Nepal earthquake of 25 April 2015 and its six aftershocks of magnitude range 5.3-7.3 are recorded at Multi-Parametric Geophysical Observatory, Ghuttu, Garhwal Himalaya (India) >600 km west from the epicentre of main shock of Gorkha earthquake. The acceleration data of eight earthquakes occurred in the Hindu kush region also recorded at this observatory which is located >1000 km east from the epicentre of M-w 7.5 Hindu kush earthquake on 26 October 2015. The shear wave spectra of acceleration record are corrected for the possible effects of anelastic attenuation at both source and recording site as well as for site amplification. The strong-motion data of six local earthquakes are used to estimate the site amplification and the shear wave quality factor (Q(beta)) at recording site. The frequency-dependent Q(beta)(f) = 124f(0.98) is computed at Ghuttu station by using inversion technique. The corrected spectrum is compared with theoretical spectrum obtained from Brune's circular model for the horizontal components using grid search algorithm. Computed seismic moment, stress drop and source radius of the earthquakes used in this work range 8.20 x 10(16)-5.72 x 10(20) Nm, 7.1-50.6 bars and 3.55-36.70 km, respectively. The results match with the available values obtained by other agencies.