 P wave

A P-wave is longitudinal, carries nonzero dilatation, and has speed $c_P=\sqrt{(\lambda +2\mu )/\rho }$ in an isotropic solid.

A P wave, or primary wave, is a type of seismic wave that is the first to be recorded by seismographs following an earthquake. Here are some key characteristics of P waves: 1. **Nature**: P waves are longitudinal waves, meaning that they cause particles in the material through which they travel to oscillate back and forth in the same direction as the wave is moving. This results in areas of compression and rarefaction.