There is quite a bit of information regarding ear tones and other precursors which I am expecting will get discussed here as time permits. For example, the same type of sound as some ear tones can be generated with pencil shape laboratory devices called "cell disrupters." Biologists use them to emulsify liquid samples.

An earthquake precursor does not have to have its origins in the earthquake fault zone itself. It could be something which happens on the opposite side of the planet from the earthquake. It may have no direct physical link with it but simply occurs before the earthquake, preferably on a reliable basis.