Near-Fault Broadband Ground Motion Simulation Applications at the Central Ionian Islands, Greece

Physics-based broadband ground-motion simulations are generated for the strong mainshocks that occurred in the region of the Central Ionian Islands, on 26th January 2014 in Kefalonia (Mw6.1) and 17th November 2015 in Lefkas (Mw6.5). The study area is associated with frequent strong earthquakes both in the historical and instrumental era. During the last decades the network of strong-motion accelerographs in the area has been densified, and thus provided an adequate number of strong ground motion records as a means to better examine the related ground motion characteristics. In the present study, broadband ground motions for the two case studies are simulated both at selected sites and at a dense grid of points covering the affected areas. The low-frequency part of the synthetics is computed using a discrete wavenumber finite element method by convolving Green’s functions with a kinematic slip model in the frequency domain. A stochastic finite fault model approach based on a dynamic corner frequency is considered to calculate the ground motions for the higher frequencies. The broadband synthetic time series are generated after merging the results obtained from the two separate techniques, by performing a weighted summation at intermediate frequencies. The simulated values are validated by comparison with both recorded Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) values and the estimated ones by using widely accepted Ground Motion Prediction Equations (GMPEs). Our results indicate that both the spatial distribution and the amplification pattern of the simulated ground motions, in the near-field, in terms of PGA and PGV are highly influenced by the slip heterogeneity and the maximum slip patches within the seismic source.