Twenty years after a 6.7-magnitude earthquake shook Northridge, Calif.,  scientists have gathered in Los Angeles to talk strategy. Los Angeles is the largest U.S. metropolitan area on an active fault line, and the question at hand isn’t whether another quake will strike, but where, when, and who will be within range. Plus, on top of all that, how much will it cost?

U.S. Geological Survey scientists say earthquakes are the most expensive natural disasters, in terms of human and monetary risk. For instance, the 1994 Northridge quake cost $15.3 billion (adjusted for inflation, that’s $24 billion in 2013 — a price tag eclipsed only by Hurricane Katrina.)

Today, seismologists worry future earthquakes will be more expensive than any before — not because there will be more movement of tectonic plates (that stays constant), but because population growth has put more people and metropolises on top of active zones. According to U.S. Geological Survey scientist Bill Leith, “It depends on where it hits. What earthquakes do is generate a lot of energy, and if that energy is directed at a major metropolitan area, it does a major amount of damage.” 

So which cities should worry about becoming the next Northridge? 

University of Colorado professor Roger Bilham has researched the cities most at risk of a “big one.” In terms of population growth vs. seismic history, residents of these cities should be on guard for lots of possible shaking, and lots of possible financial fallout:

1. Tokyo

2. Mexico City

3. Dacca, Bangladesh

4. Jakarta, Indonesia

5. Karachi, Pakistan

6. Manila, Philippines

7. Delhi, India

8. Los Angeles

9. Cairo, Egypt

10. Teheran, Iran

11. Istanbul, Turkey

12. Osaka, Japan

13. Lima, Peru

14. Lahore, Pakistan

15. Bogotá, Colombia