Three-dimensional numerical simulation of ambient seismic noise for arbitrary surface source distributions: application to the study of horizontal-to-vertical spectral ratios and their variability

This is precisely what was observed at the Volvi site, in the Mygdonia Basin in northern Greece, where the frequency of the main H/V peak can shift from 1 Hz to 2 Hz within a single day.

To better understand this striking variation, we conducted an in-depth numerical investigation of the sensitivity of H/V measurements to the spatial distribution of noise sources and to the presence of strong lateral structural contrasts. The Volvi site is indeed characterized by a particular geological setting, with a so-called "blind fault", buried beneath the surface, separating two parts of the basin with different properties.

We investigated not only H/V amplitude but also its polarization, that is, the presence of preferred directions in horizontal ground motion. This approach makes it possible to explore how source-related and structural effects can combine or even mask one another.

This work contributes to a better understanding of the information contained in ambient seismic noise measurements and of the precautions required when interpreting them. It also highlights the potential of H/V polarization, an observable that remains relatively underexplored, for characterizing complex geological structures.

References :

Gregor, D., Chaljub, E., Wathelet, M., Hollender, F., Perron, V., & De Martin, F. (2026). Three-dimensional numerical simulation of ambient seismic noise for arbitrary surface source distributions: application to the study of horizontal-to-vertical spectral ratios and their variability. Geophys. J. Int., 247(2), ggag348.