Underground rock strain release can launch surface sod upward via focusing

Evidence

Probably the best way to look at this process is to suppose that rock a hundred or few hundred meters down is under tremendous strain and then breaks away and slides a few centimeters in a few milliseconds or less. If a healthy fraction of that displacement were transmitted all at once to a spot on the surface by focusing, there is no doubt the sod would jump! — Eric J. Heller, Why You Hear What You Hear- An…, 717

Categorization

• XREF: Connects to the reader’s interest in acoustic focusing/caustics from this same book; also suggests a physical mechanism for ground effects distinct from steady waveforms.