Imagine the following scenario: After decades of warnings from seismologists, a massive earthquake strikes Tokyo in 2022 and levels wide swaths of the city, killing tens of thousands of people and leaving hundreds of thousands more missing or injured.

In a worst-case scenario for the next Great Kanto Earthquake, the Tokyo urban area, home to nearly a quarter of Japan's 127 million people, would simply cease to function.

The massive temblor would knock out all power sources and destroy key infrastructure, including railways, roads, bridges and port facilities. Haneda airport would be half submerged in Tokyo Bay, and the runways of the U.S. air base at Yokota and the U.S.-Japanese base at Atsugi, Kanagawa Prefecture, cracked open. It would only be possible to fly in immediate relief through Narita or Ibaraki airports.