Petra,

"if the sound is external or internal"

The human body is an environment within the environment. Nothing is completely "internal". That is why I asked what people mean by that. The stimulus for the eartone may be internal, but there is no reason that such stimulus could not be affected externally. My own ULF monitoring shows no relation between 1-30 Hz signals and eartones. Could be the really long-waves, I think.

"I think in the future, perhaps after predicting some large earthquakes the interest may kindle."

I doubt it. Think of the millions of people who have heard eartones since their youth and almost none have wondered about it. Your perspective is someone who wants to connect eartones and earthquakes -- my perspective is someone who just would like to understand what eartones are.

"the important issue is that to the hearer of ear tones, the sound of a small earthquake or a large one are equal. You have to hear lower sounding ear tones and understand where those belong before you can receive a much louder sound and relate it to its place. It is a learning experience."

I am a "hearer of ear tones" but I have absolutely no idea what you are talking about. Often you speak as if you are THE spokesperson for eartones, but I have never met a single person in Japan who agrees with your ideas.

"and have correlated them to resulting earthquakes."

Anyone can correlate one thing to another. That is what they do here in Japan too. Yet no one accepts your ideas here. So your ideas do not logically follow from making correlations. Not quite so simple as that.

"Sometimes you need a lot of patience"

Yes, hundreds of years from now, eartones may be understood. Probably they will be used as weapons. Too bad we won't be around for that, huh? You and Todd get annoyed at my posts, and just make me endure a terrible eartone...