A Vertical-to-horizontal spectral ratio model for India

This paper presents the results of a study on the characteristics of vertical-to-horizontal ratio (V/H) of 5% damped acceleration spectra for Indian ground motion records. Preliminary analysis indicates that at least 50% of the records exceed the Indian seismic design code considered norm of 2/3 at both the short and long period ranges. In addition, currently there are no V/H spectral ratio models available for India and the global models do not capture the trend across all the periods efficiently. Therefore, new ground motion models for the V/H spectral ratio are derived for two of the active tectonic regions of India: the Western Himalayas and the North-East India. Moment magnitude, focal depth, distance, site soil class, and focal mechanism are considered while deriving these models for a wide range of spectral periods (0.01–10s). The goodness of these models is verified through comparison with other globally available V/H models. • New V/H spectral ratio ground motion models for the two most active regions of India-the Western Himalayas (WH) and the North-East India (NE) are derived in the present study. • Comparison of estimates from the current model for the 2015 M w 7.9 Nepal earthquake highlights the goodness of the model at both near and far field sites. • Higher short period V/H ratios are observed in the dataset as well as the estimates, which exceed the 2/3rd threshold value proposed by the Indian Seismic code of design IS 1893.