[doodlebugging]

Yes they are and you are right about the rumble.

About thirty 30 years ago I was on a drilling rig in Louisiana with a geophone array deployed so that I could record the vibrations made by the drill bit as they drilled towards a potential reservoir near a salt dome. We were doing a salt proximity survey using the drill bit energy as the seismic source so that we could hopefully help steer the drill bit through the sediments beside the salt dome without sending it into the salt and possibly intersect the highest point of a reservoir rock at the salt/sediment interface so that production from that gas/oil saturated zone would be maximized since you are farther from the oil/water interface in the wet zone.

Anyway, drill bits 15000 ft in the subsurface are viable energy sources but are very low energy. We were about 5 miles from a train track but every time the trains came down the line you could see them coming when they were miles away from the closest point to the arrays. The energy would start off as a random background noise that steadily increased in amplitude until it swamped everything and was clipped in the sensors and then as the train passed it would steadily decrease until the train was several miles away.

[biotinker]

There are more practical, everyday application for that fact as well.

When I lived next to a train track, I built a seismograph to detect oncoming trains, and had a white noise machine that would ramp up volume as the train approached to prevent the train from waking anyone up.

[doodlebugging]

That's pretty awesome. There probably is a market for this since I have seen several posts on city subreddits over the years where someone is asking why trains have to blow horns, why they are noisy, why didn't anyone tell them there was a track nearby, etc.

I think you could probably sell something like this. Good luck!

[logifail]

Reminds me of this New Scientist article:

WHAT is 27 kilometres long, cost £700 million to build and can tell you precisely when trains are leaving Geneva station? https://www.newscientist.com/article/mg14820060-300-the-part...

(spoiler: the Large Electron Positron Collider at CERN)

[doodlebugging]

Great article. Thanks for that link. It is amazing to see how sensitive some of our instruments are to outside energy. I conducted gravity surveys years ago and part of the data processing always involved resolving the effects of nearby terrain since nearby density differences could contribute to an anomaly.