These recordings, as shown in the plot below, used arrays of 24 sensors spread over an aperture of 360 meters. For the sound version, just one geophone sensor plays into the left ear, and another 200 meters away plays into the right ear. You hear a pronounced stereo effect as if your ears were 200 meters apart.
The sound file loops through seven such stereo records, sped up by a factor of 10 so you hear a new record every 3.2 seconds. There are brief silences inserted between the records. In the early records you can hear traffic, passing from on ear to another; one record (plotted below) has a car and a heavy truck passing in opposite directions. The later records also have a rushing sound from a jet airliner takeoff.
(359 kb) Seven 3.2-second segments of microtremorTime increases toward the right in these plots: