What causes shock waves?

Answer 1

A shock wave is generally thought of as a compression wave that radiates from a mechanical event, like an explosion. Same thing with earthquakes. There is a compression wave in all these events. We can see a compression wave originate from something breaking the sound barrier, and that's another example. Something moving faster than sound generates the shock wave on a continuous basis, and we hear the boom! as the wave reaches us. The same thing applies in sonar when the transmitter emits a "ping" into the water. The transducer vibrates, and a compression wave is generated. Where a source of mechanical energy causes movement, a compression wave can originate and radiate. It could be argued that compression waves originate from a source of sound. That's because sound is a mechanical wave, as it is mechanical energy. Certainly it generally isn't thought of as having the power of an explosion, though. In addition to the compression waves of sound, there are the "opposite" waves. These are areas where the air is rarefied or "uncompressed" between the areas where the compression waves are traveling. A shock wave is usually the term we apply to the leading edge of a compression wave from some mechanical event. It is carrying mechanical energy outward from the cause.