Due to the new seismic legislation, the measurement of environmental seismic vibrations or seismic noise has gained considerable importance. The analysis of seismic noise measurements can be conducted using three methods: 1) Fourier spectra 2) Spectral ratios 3) H/V spectral ratios. The latter, which provides the most reliable results, is also known as HVSR (Horizontal to Vertical Spectral Ratio) method or Nakamura method. The acquisition of HVSR data, obtained using low frequency triaxial geophones, allows to accurately determine the characteristic resonance frequency of the site, an essential parameter for the correct dimensioning of earthquake-resistant buildings. Seismic microzonation studies through the HVSR measurement method have therefore become an integral and fundamental tool in the design of earthquake-proof buildings. The data acquired should be considered at the design stage to build structures with different resonant frequencies than the ground, thus avoiding the double resonance effect, extremely dangerous for the structural stability of buildings.

From a measure of resonance frequency of the ground it is possible to obtain an estimate of the Vs of the coverages, provided that the depth of the layer that generates it is known, or vice versa.
Since the stratigraphy Vs is also derived from the MASW tests, combining the results of both methodologies in the same site is an important complement of information and mutual bond, both in depth and on the surface.