My questions are about the calculation of Site Fundamental Frequency using Horizontal to Vertical Spectral Ratio (HVSR) based on Fourier amplitude spectrum:

We know that time is not considered in the Fourier spectrum. When the amplitude of the Fourier spectrum of the horizontal component at a frequency is divided by the amplitude of the Fourier spectrum of the vertical component to obtain the HVSR Curves, these two values only have the same frequency and did not occur at the same time. Doesn't this cause misunderstanding and errors in calculating the Site Fundamental Frequency?