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dear all
can you help me?
I have two HVSR registrations in a little city near Pisa (IT) that I attach here.

it's an alluvial plane, with 700 mters of clay - sand - silt.
normally the VS30 in this plain is 150 - 300 m/s

This two registrations has VS30 = 800 m/s.
IT's impossible !!!!!

near the registration site there is a wind farm with 4 wind turbine.

I find a scientific paper that said that this farm induced a frequency of 1,7 Hz.
but I think that this information doesn't explain my data.
does someone has an Idea?????

Dear Riccardo

What is the method used to obtain Vs30 in this experiment?.
I'm my little knowledge about HVSR technique you can only obtain the fundamental frequency of vibration. The only way, that i can figure out, to obtain vs30 values from HVSR is using the relationship between frequency, thickness and velocity. Well that is not the best (probability the worst) way to measure s-wave velocity profiles and calculate such important parameters as Vs30.

Until you explain in a great detail what you did to obtain Vs30 , i think nobody can help you.
My recommendation: perform a microtremor/MASW/Donwhole survey to obtain a better estimation of the velocity profile...and be careful with Vs30... if you don't want to go to jail.

Greetings.