Spectrograms - Electronic Noise
There are many signals recorded by seismic stations that are unrelated to “real” Earth processes. These include electronic spikes, cross-talk and telemetry interference associated with instrumentation. Most of these signals will appear on a single channel.
There are several examples of instrument noise in this plot. Station WIZ is dead at this time with a nearly flat trace. Spikes on station BBO (with very short bursts showing all frequencies) are due to radio interference. Station J04D has a very narrow band signal at about 10 Hz that is likely due to an instrument resonance. Such single frequency signals can be due to various sources including vibrating parts of the instrument or housing or nearby structures. In some cases, when they are seen to come and go they are thought to be due to nearby motors, generators or even moving water that causes vibrations of equipment or sturctures