Petra:

Do you always here the same pitch and background sound (before an EQ event)?

What do you mean when you say "the bg sound is closer"? Do you mean higher volume or something to do with pitch?

Would you say that the scale does not go high enough on the tone generator (in order to try and find a match).

Is Don referring to just your sounds or is Don also one that hears tones before EQs too? If Don was referring to the tones that you are hearing...then it sounds like there is a second frequency / pitch that you have not mentioned...or maybe it's hard to match since maybe it's broadband in nature.

One interesting thing to check is to await the next EQ that you had tones for and then take the seismic waveform and convert it into a *.wav file to see what it "hears" like.

If the perceived (more broadband?) background sounds matches qualitatively to what you recall that you heard...then this could be significant (since it suggests emanations from the fault where the EQ happened but before the EQ actually emerges). This may not work as the seismic Band Pass filters may wash out lots of broadband signals.... Just a LPF signal would be desired for this comparison.

Looking into hearing a ULF waveform *.wav file may also be of interest. (The GIF image of the EQ seismic waveform could be converted to *.wav file format so that you could listen to it...to see if "sounds" about the same).

It looks like this could head in the direction of Mary Maya's catalog of sounds type set-up where she describes "wine-glass"-like sounds etc. Have you read her "sounds" acronyms web-page? If so, do any of her descriptions "ring a bell" with you?

Just curious,

mark

MM's link is in one of her posts below....