A couple of days ago, I just happened to be looking at the infrasound trace from my Shake/Boom, and saw this (as it happened - no sound or apparent vibration as far as I could tell:
That is a pretty impressive sound spike. Not seen anything like that before (in the three weeks or so that I have had the system up and running). So switched over to the Z trace to see if it left any impression there:
That too is quite impressive - much bigger than the random things I see on a daily basis. It doesn’t quite match up with the sound spike though … until we look at the frequency-domain plot:
All low frequency (>10 Hz) until about the time that the sound spike occurred, then there is a corresponding “spike” of higher frequencies.
I wondered if it was a purely local event, so took a look at the data from a device about 10 miles East from me (Z - only):
Looks like he got it too.
And another station maybe 20 miles East:
Given that it is detected as ground vibrations by three stations, each around 10 miles apart in an E-W line, it looks like a local earthquake to me. But what explains the sound spike??
For completeness, this is the frequency plot of the infrasound “spike” - it doesn’t give much away, other than it being low frequency: