P-waves, and called pressure waves, are longitudinal waves, i.e., the oscillation occurs in the same direction (and opposite) the direction of wave propagation. The restoring force for P-waves is provided by the medium's bulk modulus. In an elastic medium with rigidity
where is the amplitude of displacement, k is the wavenumber, z is the distance along the axis of propagation, is the angular frequency, t is the time, and is a phase offset. From the definition of bulk modulus,
where V is the volume and is the derivative of pressure with respect to volume. Consider a wavefront with surface area A, then the change in pressure of the wave is
Bulk Modulus, Elastic Wave, Lamé Constants, Longitudinal Wave, Poisson Ratio, S-Wave, Seismic Parameter, Shear Modulus
