I have been remodeling my seismic vault to reduce noise, however I have noticed that I now have a noise line in the record between 40 and 43 Hz, before this did not happen.
Is it because the block where the RS is located is not so fixed to the ground?
Can I eliminate this noise if I add sand to the trench to make the block more stable?
This is a diagram of the installation, I hope you can guide me on this. Thank you
The high frequency end of the spectrum is where aliasing manifests itself. Could it be aliased 60Hz noise from buried electrical cables?
TideMan suggestion could be spot on. When you have time, can you try to move your Shake anywhere else on your property, to see if that line disappears?
Also, have you tried positioning the Shake on the edges of your vault instead of the central block, as an experiment to see if the line is still there once done? This could provide you with more data to understand your local conditions.
I will do it in the next few days
Today I reconnected the RS in the vault and I realized that the noise line at high frequencies has disappeared, it seems that it was temporary.
It definitely appears so, and you also have proof that the block at the center of the vault offers the best performance in local noise reduction than other places you have examined show.
Thank you also for the additional pictures of your installation!
Interesting findings. Tracking down noises can be a challenge.
Switching topics to the vault construction itself. Thanks for the pictures. It is a nice setup. However, there may be a flaw in this type of design. I had a similar isolated pier design.
We had server years of drought conditions here in Southern California and I had no issues with the vault for a little over a year. Eventually, we started to return to a normal level of rain. After a few storms, water came up through the gap between the pier and the rest of the vault. I had an underwater Shake.
Here are details of the story: A Wet Shake And Vault Overhaul - Raspberry Shake
Your conditions with water may be different. I just wanted to pass along my experience so you can be aware of a potential issue.