5. Los Angeles, USA
Metro area population: 13,131,431
Although Los Angeles doesn’t lay above San Andreas Fault line, plenty of others are hidden beneath the city. Some of them are Newport-Inglewood Fault, Hollywood Fault, and Whittier Fault, a branch of Elsinore Fault. Recent measurements have discovered helium-3 leaks from Newport-Inglewood Fault, indicating that it is much deeper than originally thought and may, in fact, be older than San Andreas Fault.
