Broadband ground motion simulations for Northeast India

This study presents broadband (BB) ground motions for two historical earthquakes ( M w ≥ 8) in Northeast (NE) India. We apply a recently developed geology-based 3D velocity model of the Northeastern region (NER) to simulate low frequency (LF) ground motions ( f < 1Hz). These synthetics are further combined with high frequency (HF) scattering wave-fields ( f > 1Hz) using a hybrid approach, thus yielding BB ground motions (0.1–10Hz). First, we calibrate the 3D model and scattering parameters by comparing the simulated ground motions against recorded data available for four events ( M w 5.2, M w 5.5, M w 6.3, and M w 7.2) in NE India. Our results indicate that the variability of the bias for spectral acceleration (SA) lies within limits [-1,1] for all four events. From the statistical analysis of the ground motion, we also observe that the hybrid approach gives a realistic estimation of site-specific BB ground motion and consistently reproduces the prominent features of the observed motions up to 10Hz at most of the stations. Next, we simulate a suite of BB ground motions to estimate ground motion intensities for two historical earthquakes (viz., 1897 Assam event, 1950 Assam event) in NE India. Our results indicate that the variations in the ground motion intensities at hard rock and soft soil sites are manifestations of the local geology and surface topography incorporated in the 3D regional velocity model. We also observe that the peak ground acceleration (PGA) for both events exceed 1 g in the epicentral region. The BB ground motions obtained from this approach will be useful to engineers in seismic design and site-specific hazard estimation. • Broadband ground motion simulations for Northeast India using hybrid technique. • Efficiently handles the topography, and 3D variation in the material property. • Broadband synthetics are sensitive to the choice of scattering parameters. • Statistical analysis is conducted to evaluate performance of broadband synthetics. • Ground motion estimates can be used in construction of existing and new structures.