A 1-inch geophone on my basement slab just caught a mighty freight train passing about 1/4 mile away. I logged the night, found the event corresponding to my 3:34 AM eyewitness confirmation, and the seismic signal jumps dramatically. Next step: spectral analysis—how much of that ground motion is below 20 Hz? https://salemdata.net/johnpress/?p=1276 #Geophone #Seismology #Infrasound #ESP32 #DIY #DataCenters #SalemOR