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In the present study, a hypothetical earthquake of magnitude 8.5 has been simulated using the modified hybrid technique. Existing hybrid technique, as the name suggests, is the blend of two already existing simulation techniques, i.e. composite source technique and the envelope technique. In the present modified technique, site response functions and high-frequency decay parameter (kappa factor) have also been introduced in the existing hybrid technique. The waveforms have been simulated at more than 430 points using the calculated site response or transfer function estimated at 50 recording stations situated in the central seismic gap (CSG) region of Himalaya. Peak ground acceleration (PGA) and duration parameters have been estimated. Calculated PGA values helped estimating in the corresponding intensity for those PGA values at various stations. With the help of these PGA and intensity values, the scenario hazard map has been prepared for central seismic gap (CSG) region of Himalaya. It has been found that the stations situated close to rupture initiation point is ≥ 1 g. The estimated PGA values have been compared with the PGA values of other studies. The earthquake has been simulated using three different rupture points The station having highest PGA values changed with rupture initiation point. The intensity values are correlated with the damage pattern of region and therefore relatively more useful for agencies involved in the mitigation of seismic hazard of the region. Accordingly, the synthetic intensity maps have been generated in the present study by converting PGA values into MMI values using an empirical relation. The comparison with the other studies shows an agreement with the other studies. This modified technique is independent aftershocks database and velocity-Q structure. This research work will help bringing light on the effect of site response functions and kappa factor. This kind of study can help in mitigate the earthquake hazard and design an earthquake-resistant structures and building for that particular area. [ABSTRACT FROM AUTHOR]

In the present study, 1991 Uttarkashi (M 7) and 1999 Chamoli (M 6.6) earthquakes that occurred on October 19, 1991, at 21:23:14 h and March 28, 1999, at 19:05:11 h, respectively, have been simulated using the modified hybrid technique. Hybrid technique is the combination of two existing techniques, i.e., envelope technique and composite source model technique. In the present modified technique, site amplification functions and kappa factor have also been incorporated. The simulated waveforms and their corresponding response and Fourier spectra for each site have been generated. In this study, simulation has been done at 11 and 9 recorded stations of Uttarkashi and Chamoli earthquakes, respectively. Important frequency- and time-domain parameters, i.e., Fourier spectra, response spectra, peak ground acceleration (PGA) and duration at stations, have been estimated and compared with the observed accelerograms. It has been observed that the simulated PGA (231 cm/s2) at the closest distance Bhatwari (22 km) matched with the observed one (248 cm/s2) for the Uttarkashi earthquake. The same has been observed at the nearest most station Gopeshwar (19 km) of the Chamoli earthquake. The simulated PGA (347 cm/s2) for this station has been found well matched with the observed PGA value (352 cm/s2). Similar matching has been observed for other stations also. The present technique is independent of velocity-Q structure of earth's layered model and past events data of small earthquakes. This study brings light on the site effect and high-frequency decay parameter. This study can be very helpful in the estimation of seismic hazard in a specific region and designing earthquake-resistant buildings. [ABSTRACT FROM AUTHOR]