Hi Don, buenas tardes. As far as a “centralized database” goes, I’m not aware of one either, but that doesn’t mean it doesn’t exist somewhere. The following post is a good example of a man-made (or rather, machine-made) signal in SWARM spectrogram view. Many people find that it’s much easier to figure out what is causing noise at a given station by looking at both the spectrogram and the seismogram (i.e. the standard line plot) together. I find the spectrogram to be immensely useful as a visual aid to help me figure out the source and character of the noise.