Effects of cavities on seismic ground motion

Within the studies about the topographical and morphological effects on the earthquake ground motion, the interest is growing whether the motion could be locally influenced by the presence of natural and anthropic cavities. To this aim analytical models and 2D numerical analyses suggest that amplifying effects on the horizontal component are expected above the flanks of the cavities while attenuation effects are expected in the zones overshadowed by the cavities. The paper illustrates the results of a set of 2D numerical analyses performed with the FLAC code to investigate the importance of the main factors involved in the diffraction of seismic waves by a cavity: size and embedment depth, prevalent wavelength of the incident motion and incident angle. Some simplified amplification/deamplification charts have been obtained in terms of adimensional parameters in frequency domain that can be used for engineering applications