Alternative regional ground motion models for Western Himalayas

The present study aims at developing a ground motion model (GMM) for the 5% damped horizontal spectral acceleration, using regression analysis of strong motion records available for the Western Himalayan region. In addition to developing a model using just the regional data, the study also explores three different methods to derive a GMM that can circumvent the limitation of near field data shortage in the Himalayas. The alternatives explored in this study include calibrating a global model to the regional dataset; deriving a GMM by appending a dense near field foreign dataset to that of the regional data; and deriving a near source correction factor to the regional model. These models are applicable for shallow crustal earthquakes of magnitudes between Mw 4.0-7.9 and depth up to 45 km over distances up to 960 km. The efficacy of each of these models is established through comparison with the recorded data and with other regional GMMs. Moreover, the best model among the four proposed GMMs is verified through derivation of rankings based on quantitative analysis of residuals that were obtained between the observations and the respective estimates.