Historical records claim the mountains and rivers literally traded places. The earth opened in crevices up to 20 meters deep, swallowing entire communities in the pitch black of a freezing winter night. By dawn, the geography of an entire region had been rewritten.

This episode is a forensic breakdown of the 1556 Shaanxi earthquake, the deadliest in recorded human history. We examine the half-graben geology that triggered it, the cave homes that became tombs, and the chilling truth that most of the hundreds of thousands of victims didn't die from the shaking itself.

• The 'trapdoor' rift geology of the Wei River Valley and the fault scarps still 2-8 meters high nearly 500 years later
• Why loess-carved yaodong cave homes, brilliantly insulated, liquefied and collapsed instantly under Mercalli XI shaking
• The math behin ...