Deterministic Seismic Microzonation of the NCT-Delhi (India) and Earthquake Engineering Implications

A deterministic seismic microzonation of the NCT Delhi (The capital of INDIA) and its earthquake engineering implications is presented in this paper. The NCT Delhi with population density around 21,000/sq. Km has experienced several severe earthquake shakings in the past due to earthquake occurrences in its vicinity and in the Great Himalaya. The exposed central quartzite ridge, Badarpur-Okhala hillocks and River-Yamuna are responsible for the very large spatial variation of sediment thickness (10 m to more than 300 m) in the NCT Delhi. The dynamic properties of sediment layers over the quartzite basement at 158 sites, well distributed in the NCT Delhi, are considered for seismic microzonation. First, we have finalised the maximum credible earthquake (MCE) for each considered site based on the deterministic seismic hazard analysis. Thereafter, acceleration time history at basement level is computed at each site using stochastic finite-fault method with dynamic corner frequency and the geometry as well as rupture-dimension of the respective MCE. The basement ground motion is numerically transferred to the free surface using the rheological parameters and thickness of sediment layers overlying the quartzite basement. Different maps of earthquake engineering interest like peak ground acceleration (PGA), peak ground velocity (PGV) and peak ground displacement (PGV) at basement level and the free surface level are developed and analysed for earthquake implications. The obtained range of PGA (0.08-0.30g), PGV (3.34-26.58cm/s) and PGD (0.55-7.2cm) at the free surface and fundamental frequency of the sediment deposit (0.4-7.0Hz) reveals that the NCT Delhi needs special attention by the planners, engineers and decision makers for earthquake disaster preparedness.