Two sub categories exist that are relevant to the source of the seismic signal.

Lahars can be detected seismically, as they cause a high-frequency seismic signal.

But machine learning—training computer algorithms to analyze large amounts of data to look for patterns or signals—suggests that some of the small seismic signals might matter after all.

An elephant running or mock charging can create seismic signals that can be heard at great distances.

These seismic signals usually have the period of 6 2 seconds.