This test allows determining the fundamental or predominant period of the soil (To) using the H/V spectral ratio method. For site effect studies or microzonation, this data is very useful to estimate where and how the soil will amplify the acceleration response spectrum.

This parameter will soon be incorporated and required in the Seismic Standard and must be evaluated mandatorily for the seismic classification of the soil or foundation ground.

In seismic structural design, it is usually assessed through modal spectral analysis, which depends on the conditions of the study site, making this data highly important.

Using the spectral ratio between horizontal and vertical waves (HVSR), the frequency and therefore the fundamental period of an area under study are obtained. By taking measurements with a surface triaxial seismic sensor and applying the Nakamura Method, these values can be determined, allowing estimation of the seismic wave amplification potential, commonly known as the site effect.

The objective of this test is to determine the fundamental or predominant period of the soil (To). Data is recorded at various points on the site for a minimum duration of 30 minutes. It is important to note that the results of the curves used to determine the fundamental period do not always meet the frequency and amplitude recommendations established by the software, a situation that must be evaluated by a specialist who will interpret and analyze the measurements and results accordingly.