Historical accident put one of the world's biggest cities (23m) on such dangerous ground.

是历史偶然将这个世界上最大城市之一(2300万人口)放在了这么危险的地方。

youdao

Sections of a drill which broke through the roof of a rail tunnel came from a construction site above the ground, accident investigators have found.

BBC: Construction drill came from site above rail tunnel

Mr. BARIMO: There were a handful of accident causes that stood head and shoulders above all the others, things like flying airplanes into mountains or into the ground.

NPR: For Air Travelers, More Safety and More Problems