[Publius6961]

You don't want to be within 30 miles of a "Castle Bravo" 15 megaton firecracker. At optimum blast height, that distance left islands burnt to a crisp before the shock wave blew the burning trees out to sea.

I would not want to be within 100 miles. But at that distance it would be a low rumble and little else, either physically or symbolically.

[Cyber Liberty]

Correct. The force of the explosion diminishes rapidly as you move out from the epicenter (inverse of the distance squared).

Also, the thunder would be, let see....100 miles, 5 seconds (roughly) per mile, so about 8 1/2 minutes after the "pop".