back where i used to live was a cave
it was fun to go there and scare younger kids to go in on a dare,

some 20 years later i suppose kids were still doing that and some rocks fell and killed 2,

so the city decided to do something about the cave,
the rigged it with explosives to cave in the cave,

the blast was so extensive that it created a ripple that registered as an earthquake.

one single jolt was felt miles away cracking streets sidewalks and damaging building walls,

maybe your BOOM was also an underground explosion.