Re: sound waves in water

[Charles Steele <chasst@xxxxxxxxxxxx>]

Tony and Dick are correct. but a more general view comes from considering a solid. For the infinite medium, there are pressure waves (p-waves) and shear waves, which travel a little slower. For the viscous fluid, including air, the p-wave is the "sound" wave. The shear waves reduce to  boundary layer effects, so you do not see much of these. The seismologists know that the earth's mantle is solid because the shear waves get through, while the earth's core is  fluid since the shear waves do not go through.

In addition in the solid, you have free surface waves (Raleigh waves) that propagate slower, and usually cause the big damage in earthquakes. There are somewhat similar waves (Stonely, etc.) that can propagate along interfaces between materials of different properties.  These surface waves also occur in fluids. In the cochlea, the interface wave is the "slow" traveling wave, which causes a displacement of the basilar membrane, while the "fast" wave is the p-wave, which causes little displacement of the basilar membrane.

So for an sound source in the ocean, 3-D spherical  sound waves are generated which hit the free surface. A portion of the energy is reflected, and the rest converted into (nearly 2-D) surface waves. So at some distance from the source, what you measure is mainly the slow surface wave. Watching the surf, you are seeing the surface waves (modified by the shallow depth), and little of the sound waves.

Charles Steele