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Hello,
Is it possible to have an H/V curve with its fundamental frequency (fo) greater than 1 Hz but having a natural origin? I have analyzed the Fourier spectrum and applied the "Random Decrement" technique to my H/V curve and both indicate that the frequency (fo) is of natural origin. This result is contradicting the SESAME guidelines where they indicate that frequencies greater than 1Hz are of human origin.
I hope you can clarify my doubt or recommend some paper to read.
Greetings.

Effectively, anthropogenic sources are usually above 1 Hz. There are also natural sources which produce noise above 1 Hz (waves close to a shoreline, wind in a small tree,...). f0 above 1Hz are common for sites with soft and superficial layers.

A source can be non-natural (passing cars,...), but at a sufficiently long distance, the spectral ratio is controlled by the ground structure. Random decrement technique is used to detect peaks produced by close-by sources which are repetitive. The phase remains absolutely constant over time. Usually the peak on the HV in such cases is very sharp and narrow band.

When the bedrock/reflector is at small-medium depth it is very likely that it produces an H/V peak with a frequency >1Hz which has non-anthropogenic characteristics verifiable both by the power spectrum and by the application of Ramdondec.

Luigi