[Reventlov]

There is not really a sonic "boom": the sound you hear is shaped as a cone (behind the plane) so it's continuous and emitted as soon as the plane is supersonic. You only hear it one time because you're static, hence the "boom" (everyone on the path of the plane will hear it at different times). A supersonic plane is very loud, and if you're static it sounds like some explosion ( https://www.thelocal.fr/20200930/loud-bang-heard-in-paris-wa... for a "recent" example).

Usually military plane avoid going supersonic close to cities.

Extract from wikipedia:

  A sonic boom does not occur only at the moment an object crosses the speed of sound; and neither is it heard in all directions emanating from the supersonic object. Rather the boom is a continuous effect that occurs while the object is travelling at supersonic speeds. But it affects only observers that are positioned at a point that intersects a region in the shape of a geometrical cone behind the object. As the object moves, this conical region also moves behind it and when the cone passes over the observer, they will briefly experience the boom.

[fanf2]

Another example was January this year when a couple of RAF Typhoons intercepted an unresponsive civilian plane, and their sonic boom was heard over large parts of southeast England https://www.bbc.co.uk/news/uk-england-essex-55645967