When I get waveforms such as the attached, are these considered within a normal reading? Would they represent some time of abnormal vibration?
I don’t know that you can always determine what these things are.
What you are looking at there is sound (infrasound) - air pressure. Could be as simple as someone opening or closing a door. I did check where your station is located, and it looks like a pretty quiet area, but then so does mine. However, I see a significant difference between night and day, both in ground vibrations (Z-channel) and infrasound (F-channel).
Where I start, it to look at both F and Z channels to see if whatever it was affected both. If it did, at least in this area, for most things, both means fairly local. There is some construction work about a mile away, I see some signals which I attribute to the heavy equipment being used there on the Z channel, but it doesn’t show on the F channel.
Then, sometimes I see something like this (F-channel):
and on the Z-channel):
So what can we think of that makes a fair amount of low frequency sound and shakes the ground too?
Well, around here, it’s usually a helicopter. If we take a look at the same signals in the frequency domain, we see:
F:
Z:
The doppler shift you see there is pretty much a give-away.
Light aircraft don’t seem to shake the ground, you only see a sound trace, no Z signal at all, but the doppler shift is there.
One that took me a while to realize what it was was the weekly trash collection. The sound of the heavy diesel truck stopping and starting, lifting and dumping the trash cans as it moves along the road … it vibrates the ground as well as making a noise.
Trying to determine the origin of some of these can be quite interesting. But you are not going to determine the origin of all of them.
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Just saw/heard this one go over:
FlightRadar gives me an ID:
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