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Alternating
compressions (“pushes”) and dilations (“pulls”) which are directed in the
same direction as the wave is propagating (along the ray path); and
therefore, perpendicular to the wavefront.
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VP
~ 5 – 7 km/s in typical Earth’s crust; >~ 8 km/s in Earth’s mantle and
core; ~1.5 km/s in water; ~0.3 km/s in air.
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P
motion travels fastest in materials, so the P-wave is the first-arriving
energy on a seismogram. Generally smaller and higher frequency than
the S and Surface-waves. P waves in a liquid or gas are pressure
waves, including sound waves.
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