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A body wave caused by oscillation of a normal stress in a matter and as such resulting in strain oscillations along the direction of p-wave propagation.
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P-wave can propagate through gases, liquids or solids and moves faster than other body waves (almost twice faster than s-wave).
When all body waves are excited at the same time the p-wave is the first arrival to the sensor, hence the name "primary".
See also
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Physics / Mechanics / Continuum mechanics / Mechanical waves / Body wave
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