Dear Atratus, welcome to our community!
This is indeed a very interesting project, and I think that this topic here:
can help you with what you want to plot spectrograms from the data you are recording with your Geophone. This would require some Python knowledge, and we have some basic code you can use as a starter in our manual, here: Metadata - Instrument Response Files, and here: Developer’s corner
You can also download the SWARM software (created by the USGS) here: USGS: Volcano Hazards Program and see if you can successfully interface your sensor with it. You will then be able to see data in real-time flowing from your Pi and have access to spectrograms which the program will automatically create for you.