Hybrid Broadband Ground Motion Simulation for 2015 Mw 7.9 Nepal Earthquake

The present study aims at simulating broadband ground motions in the epicentral region of the 2015 Mw 7.9 Nepal event, using hybrid broadband technique. The spectral element method is used to simulate the low-frequency ground motion. The three-dimensional material property variation and the basin geometry at the Kathmandu basin are incorporated in the spectral element model. High frequency synthetics are simulated using scattering Green's function approach by consistently using the source and medium model of low frequency simulation. The simulated Low Frequency (LF) (0-0.3 Hz) results are combined with high-frequency scatterograms to generate broadband ground motions (0-10 Hz). The scattering parameters for broadband ground motion simulation are estimated from the recorded data of Nepal mainshock. These parameters are used further for simulating the ground motions over a grid of stations at 2 km x 2km spacing at the epicentral region. The simulated results are shown as peak ground acceleration (PGA), peak ground velocity, and spectral acceleration contours plots. The maximum PGA in the horizontal and vertical directions are 0.35 g and 0.32 g in the epicentral region. Also, the acceleration time histories and corresponding response spectra are presented for some of the selected cities in the region where no records are available. These simulated outcomes are used for analyzing the validity of Indian seismic codal provisions at the near-field of large Himalayan earthquakes. The results show the significant underestimation of near-field hazard by the codal provisions at the Himalayan region.