A magnitude 7.6 earthquake 1,500 miles away caused 4 ft high waves at Devil's Hole: https://www.cbsnews.com/news/mexico-earthquake-triggers-4-fo...
It may be that the aquifer in Devil's Hole is somehow connected to a network of underwater aquifers thousands of miles away in Mexico… but we just don't know, and have no way of knowing right now.
> Earthquake-generated seiches can be observed thousands of miles away from the epicentre of a quake.
https://weather.com/news/video/how-mexicos-earthquake-caused... says the waves started about 20 minutes after the earthquake, which was 1,500 miles away. That's about 2 km/sec, which makes it (I think) due to the S-wave.
It's certainly not underground water being compressed for hundreds of miles before arriving at Devils Hole, if only because underground water flow doesn't work that way.
Seiches happen even in swimming pools, as at https://www.youtube.com/watch?v=-2JwUSD3x2s where the pool starts sloshing around from an earthquake about 200 miles away. They don't need to be connected to a larger water system.
I see from https://en.wikipedia.org/wiki/Devils_Hole :
> The pool has frequently experienced activity due to far away earthquakes in Japan, Indonesia, Mexico, and Chile, which have been likened to extremely small scale tsunamis
and https://home.nps.gov/deva/learn/news/alaska-quake-shakes-wat... notes the Alaska earthquake was 2,000 miles away in the other direction.
The safest class of substances I can think of are unusual isotopes.
They're chemically identical to the regular elements, which is what matters for life forms, but can be detected by scientific instruments.