"Among the Cook recordings, not listed in their online catalog but available nonetheless (telephone 1-888-FOLKWAYS) is Cook Laboratories Catalog Number 5012. The Smithsonian's internal listing calls it simply "Earthquake," but it is actually a full transcription "Out of This World," with earthquakes on a 20-minute-long track 1 and ionospheric noises on a 20-minute-long track 2.
"Earthquake" is not an audio recording of the actual sounds that would be heard by a human being on an earthquake site. It is more cerebral than that.
In the 1950s, Hugo Benioff of CalTech devised a seismometer that recorded seismometer data on analog tape at a speed of 0.02 inches per second. The "Earthquakes" side delivers of the results of playing these tapes at standard playback speeds, speeding them up by factors of 187 to 750 times normal speed and converting subsonic earthquake vibrations into audible sound. The results are intriguing, indescribable, and curious to hear. Nearby earthquakes have a fairly sharp and brittle sound; distant ones sound dull and echoey.
The original LP contains a very strange track in which an earthquake recording is reproduced "to within 2 or 3 times original speed" and at a high amplitude. The narration notes that you will not be able to hear much of anything, but if you bend over and watch the tonearm you will be able to see it move. In fact, few tonearms, apparently including the one used by the Smithsonian to transcribe this segment, are able to play this band without skipping grooves.
The second side of the LP, "Sounds from the ionosphere," records the sounds that are heard when an antenna, with its signal suitably filtered, is connected to an amplifier rather than to a radio receiving set. The propagation characteristics of the ionosphere cause different audio frequencies to propagate at different speeds. The result is that the impulse created by a static discharge is heard, not as a click, but as a descending or ascending whistle. The sounds on this recordings are strange, melodious--almost like a mass of birds or spring peepers--and literally unearthly.
(If the ionospheric noises on Cook catalog #5012 are not enough, the Smithsonian also has Cook catalog #5013. This is a stereo recording combining ionospheric noises recorded simultaneously in Hanover, NH and Washington, D. C.)"