Slideshow presentations from the workshop program described in our EduQuakes column, organized in three phases: “Earthquakes: Why and How They Happen,” “From Seismic Waves to Sound Waves,” and “The Chorus of the Earth.”
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Slideshow S1. Earthquakes: Why and How They Happen. We explain the origins of plate motion. We show how the associated forces lead to deformation in narrow zones at plate boundaries and in diffuse networks of faults in continental interiors. We show how the energy released by an earthquake is carried through the Earth by seismic waves. We then describe P, S and surface waves, showing how they appear on a seismogram and how humans perceive each type of wave, particularly in the near-field.
Download: Earthq-why-how.zip [Zip Archive of 10 PNG Images; ~6.5 MB].
Slideshow S2. From Seismic Waves to Sound Waves. This section shows the essential knowledge about waves. We explain that a wave represents the transport of energy, and that P waves carry energy in the same way that sound does, even though in the former case the source of energy is the earthquake, while in the latter the source may be our voice or an instrument. The Wave Lab (a tone generator and signal analysis software) first generates monochromatic sound waves at different frequencies, from the centre to the limit of human hearing, then it analyzes the sounds from different tone of voice (adult males, adult females and children) and instruments (xylophone, diapason or any available). We show that the longer is the instrument, the lower is the frequency, and the shorter the instrument the higher the frequency. A similar relationship exists between body mass and vocal fold size of an animal and the fundamental frequency for flow-driven vocalization (voice).
Download: Seis2sound-waves.zip [Zip Archive of 21 PNG Images; ~4.9 MB].
Slideshow S3. The Chorus of the Earth. Very low frequency waves are emitted by the Earth, in
the range 10-7 Hz - 50 Hz. They are out of hearing range of humans.
We compare the natural vibrations of the Earth with the five groups of a
polyphonic chorus: soprano, contralto, tenor, baritone, and bass. The public
comes to realize that the seismometer is our artificial ear, which hears
the waves outside the human hearing range. These examples underline that
natural physical phenomena are very close to our daily experience and
perception.
Download: Chorus-Earth.zip [Zip Archive of 14 PNG Images; ~5.3 MB].
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