Revisiting the 1995 MW 6.4 Aigion, Greece, earthquake: Simulation of broadband strong ground motion and site response analysis

The 1995 MW 6.4 Aigion earthquake is one of the largest and most destructive seismic events that have occurred in Greece over the past few decades. The ground shaking in the near-fault region was recorded by a strong-motion accelerograph in the city of Aigion, at a distance of about 16 km from the epicenter. The recorded horizontal ground acceleration exceeded 0.5 g, whereas the horizontal components of ground velocity exhibited pulse-like motions of large amplitude. These ground-motion characteristics have been attributed to forward rupture directivity combined with the effects of soil and topography. In this article, broadband synthetic ground motions are generated at selected locations and at a dense grid of observation points extending over the causative fault of the 1995 Aigion earthquake using a hybrid deterministic-stochastic method. The low-frequency components of the synthetic ground motion are simulated using the discrete wavenumber method and the generalized transmission and reflection coefficient technique, whereas the high-frequency components of the synthetic ground motion are generated using the stochastic modeling approach and the specific barrier model. The two independently derived ground-motion components are then combined using matched filtering at a crossover frequency of 2 Hz to generate broadband ground-motion time histories and response spectra. The effects of soil and topography on the simulated ground motion in the city of Aigion are also investigated through site response analysis. In addition, the strong motion recorded at Aigion is corrected for crustal anisotropy using the cross-correlation technique, thus further enhancing the alignment of recorded and synthetic ground-motion time histories. Finally, the synthetic ground motions are compared with ground-motion estimates obtained from observed geotechnical damage, USGS ShakeMaps, and ground-motion prediction equations.