Seismic amplification on surface is the main reason of the damages caused by earthquake. The effects can be further aggravated in the case of “coupling” between modes of vibration that occurs when the resonance frequency of the subsoil coincides with that of the buildings. For this reason, in design time, it must be performed a careful analysis of the characteristic frequencies of the sites.

The analysis of the environmental seismic noise allows to obtain important informations about the subsoil resonance.

The environmental seismic noise is the set of all vibrations on the surface generated from natural sources or anthropogenic ones (dynamic land activity, vehicular traffic, industrial activity, etc.)

Through the use of a particularly compact and easy instrument, which is Digital Tromometro (Tromino), it’s possible carry out in-depth studies about Seismic Effects on site (Microzonazione Sismica).

This instrument consist of a electronic control unit and a three components geophone (velocimeters) for recording environmental microtremors in the range of frequencies between 0.1 and 200 Hz. Furthermore, it’s equipped with a compass to orient the recording instrument so that its major axis is suitable oriented.

The acquired records are processed through the use of a specific software that allows to perform spectral analysis of vibrations and the definition of curves H/V for the analysis of site effects.

The HVSR technique, very rapid and effective, is totally non-invasive, which means that it doesn’t require any type of perforation and even seismic cables or external sources different from the environmental noise. For this reason, it can easily be applied everywhere.

The environmental seismic noise recording inside buildings can be used to identify natural frequencies of vibration; the acquisition and processing methods change, but the instrumentation remains exactly the same.