4. Earthquake Signal converted to Sound

On March 06, 2005 two earthquakes were recorded within an hour of each other.  Both were generally north of Ohio, one in the Russian Arctic almost directly north of Ohio and the other in the Gaspe region of Canada to the northeast.  The Russian earthquake was more distant but roughly one magnitude greater in terms of the energy released.  The seismograph shows the effect of distance on the two signals with the energy being dispersed and dampened.

I wondered what these earthquakes would sound like if we could hear them.  The frequencies of earthquakes are too low for us to hear but they can easily be increased with the appropriate computer processing.  I imported the raw data file for the seismograph shown into a program called SciLab as a vector.  I did this conversion years ago and thought these data were sampled at a frequency of 20 samples/sec.  I then used a standard SciLab function to convert the vector into a wav file that could be heard by increasing the sampling rate to roughly 22,000 samples/sec, speeding it up about 1000 times. However the length of the recording and the length of the record in the display indicate a factor of 852 times and the sampling rate shown for the wav file indicates a factor of about 400.  Whatever the actual factor, the difference between the two earthquakes is apparent.

The sound is best heard on a sound system having a sub-woofer, with the bass control turned to maximum.   Click the icon to the left to listen to the results of the conversion, noting the predominance of the low frequency components on the Russian earthquake compared to the higher frequency components in the closer Gaspe signal.

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