Strong ground-motion prediction and uncertainties estimation for Delhi, India

An endeavour has been made in the present study to estimate the uncertainties in strong ground-motion estimation for Delhi region. The strong ground motion (SGM) has been estimated using the logic-tree approach with equal weights chosen for the branches of the logic tree because a scientific preference has not yet been developed for the area. Coefficient of variation (COV) maps have been generated along with the mean SGM which aid in visualizing the effect of our lack of knowledge on the final results and highlight those areas where improved scientific understanding can have an impact on future hazard maps. Monte Carlo simulation has been sued to consider the effect of the variation in the seismic hazard parameters. The spectral ground generated for various return periods suggests higher values in the north-west region with a decreasing trend towards the south-east part of Delhi. The hazard gradient is highest at spectral acceleration (Sa) 0.1 s and lowest at spectral acceleration (Sa) 1.0 s for all return periods. The highest COV values (~0.60) were observed in case of PGA while lowest COV values (~0.15) were observed for spectral acceleration (Sa) 0.3 s at all return periods. One of the conspicuous observations is that the trends of COV maps have been found to be governed by the boundaries of the seismogenic sources. While COV values are governed mostly by Line Sources in smaller return and time periods, in higher return periods trend of the COV maps were found to be governed by the boundaries of the Areal Sources.