Skyquakes

[UM-Bot]

http://www.unexplained-mysteries.com/images/newsitems/winterclouds.jpg

William B Stoecker: We live for the most part on the surface of the land, although we travel through the sky and on the surface of the sea. Rarely do most of us venture underground, and never to any great depth. Only two men have been to the deepest trench in the sea, and only a handful have ventured far beyond our atmosphere. And strange and sometimes frightening mysteries emerge from under the sea, under the Earth, and, especially, from the sky. It is in the sky (and sometimes emerging from or entering the sea) that we see UFOs. Blocks of ice, fish, frogs, and other things fall from the sky, with no explanation. And then there are the “skyquakes”…loud, booming sounds, rather like cannon fire, with no known origin.

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[zooage]

I've always called it thunder. It's known to occur when ever there are clouds present.