Reflection seismic is a method of geophysical analysis of the subsoil that allows to detect with high precision the characteristics and the geometry of the rock formations underlying the earth's surface.
The HVSR, or Nakamura method, allows to highlight the possible resonance frequency of a soil. This value is calculated by making the ratio between the average of the horizontal spectra on the vertical spectrum (H / V) of the natural vibrational signal.
In structural engineering, modal analysis uses the overall mass and stiffness of a structure to find the various periods at which it will naturally resonate. These periods of vibration are very important to note in earthquake engineering.