Spectral attenuation models in the Sikkim Himalaya from the observed and simulated strong motion events in the region

Strong motion recordings by the Sikkim Strong Motion Array (SSMA) of 80 events with good signal-to-background noise ratio (greater than or equal to3) for magnitude between 3 to 5.6, have enabled estimation of source model and site response, and also the simulation of spectral acceleration for moderate-to-large earthquakes with 6 less than or equal to M-W less than or equal to 8.3. A combined simulated and recorded data set have ultimately been utilized for deriving the spectral attenuation laws incorporating the local site conditions, namely, topographic effect and site response, with and without shear wave velocity in addition to the normal earthquake parameters, viz. moment magnitude (M-W) and source-to-site distance (r). The spectral attenuation laws developed in this study have been found to be appropriate for predicting free-field horizontal Peak Ground Acceleration (PGA) for earthquakes of 3 less than or equal to M-W less than or equal to 8.3 and for the sites with distances up to 100 km from the source in the Sikkim Himalaya. The estimated spectral acceleration through these attenuation laws mimic the mean spectral acceleration simulated using Brune's source model.