Spectrograms are a different way of presenting seismic waveform data for human review and interpretation. Similar to seismograms they show seismic energy versus time, but also include information about the frequency content of the seismic waves. For a complete description of spectrograms, with keys to their interpretation, including examples see "What is a Spectrogram."
We have grouped spectrograms into geographic regions to monitor three types of seismic sources. The source types are: