Regional Earthquake

This is a regional earthquake -- one that occurs less than about 300 kilometers from a seismic station. On account of the relatively short distance traveled by the seismic waves, they are still rich in high frequencies. Consequently, you hear sharp onsets for the P- and S-waves. The longer the seismic waves travel, the more attenuated high frequencies become, so the sound shifts to lower frequencies.

You hear two distinct arrivals: The P- and the S-wave arrivals. They're marked on the seismogram shown. The two arrivals have distinctly different pitches. The P-wave is richer in higher frequencies, so it sounds like the rap of a wooden bat when it hits a ball. The S-wave energy is more attenuated, depleted in high frequencies, and so sounds like the boom of a drum. Following the S-wave arrival is a longer, spread-out surface wave arrival. The surface wave lasts around 75 seconds, so you hear a rumble corresponding to its arrival. It is lower in frequency than either the P-wave or the S-wave.

So that you can hear the difference better, the seismogram is repeated three times in the audio track.
Regional earthquake