S T G Raghukanth

The present study aims at developing a new strategy to model the spatial variability of slip on the rupture plane using multi-dimensional ensemble empirical mode decomposition (MEEMD) technique. Here, the earthquake slip distribution is split into finite number of empirical modes of oscillation called the intrinsic mode functions (IMFs). This help in identifying the fluctuation component and trend in the slip data. The trend is positive and characterizes the nonstationary mean of the slip distribution. The fluctuation component can be modelled as a stationary random field using an exponential power spectral density function. The trend can be modeled as an elliptic patch. This new technique is demonstrated for the slip distribution of the recent Nepal Earthquake, 2015. It is observed that the new model can be used to simulate the spatial complexity of slip distribution of any earthquake.

The spatial distribution of seismic site coefficients at Guwahati is presented in this article. Estimated site coefficients consider different site types in the city and several level of ground shaking consider average of probable seismic event. The evaluation of site coefficients is based on the standard penetration test data at 105 boreholes distributed over the city. Equivalent linear one dimensional site response analyses are performed to predict the site amplification and to determine the spectral acceleration response. Due to the unavailability of recorded ground motion data for the region, synthetic ground motions simulated at the bedrock level for the city corresponding to several combinations of magnitude (Mw) and source-to-site distance (R) are used as input excitation. Simulated synthetic ground motion data with varying levels of excitation have been used to take care of the uncertainties in the input ground motions. The analyses depict the modification of the seismic ground motion due to the presence of soil overlying the bedrock.