Are seismic waves and shock waves same?

Question

Are shock waves (those produced by high speed jets) and seismic waves (produced during earthquake) the same?

In many places I have seen seismic waves referred to as shock waves. So are these two same?

Answer 1

In physics a shock wave refers to a disturbance that is moving faster than the speed of sound in the medium. This happens when an object travels faster than the speed of sound in the medium - and such a shock wave builds considerable pressure.

In an earthquake the wave is moving at the speed of sound. While it is possible that a fracture event propagates faster than the speed of sound (crack tip velocity in an already stressed medium, for example) this is not necessary to initialize a big wave through the earth’s crust. However, the event that causes the wave is a “shock”, so it is often called a shock wave.

But it’s not the same thing.

Answer 2

I agree that there is misuse and confusion in terminology in a lot of the literature. Seismic waves result from shock waves, but move through solid (and liquid, in the sea) material, namely the earth, as oppose to shock waves in air. Both result when an object moves through the air/earth faster than sound does. When referring to the earth exclusively, seismic waves and shock waves can be used synonymously (but care should be taken as mentioned below).

Shock waves in air are almost always longitudinal in nature. Seismic waves can be referred to as shock waves but come in two basic categories:

• Body waves which propagate through the interior of Earth, and include:

1. Primary or P-type waves which are longitudinal.

2. Secondary or S-type waves which are transverse.

And

• Surface waves which as implied, propagate along the surface of the earth and surface waves are also mechanical waves that come in roughly four types:

1. Love waves (L waves) which are transverse waves.

2. Rayleigh waves which have both transverse and longitudinal modes of propagation.

3. Stonely waves is an interface wave propagating along a solid-fluid boundary or along a $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ $ solid-solid boundary.

4. Normal modes are standing waves that come from the interference of wave types above.