Southern California Long Overdue for Massive Quake, Experts Say

And the results of such a quake would be devastating.

"A large earthquake would likely kill thousands and cause billions of dollars in damages," said Lucy Jones, a seismologist with the U.S. Geological Survey.

Jones serves as chief scientist of the Southern San Andreas Earthquake Scenario, a team of scientists assessing potential earthquake scenarios in an area of Southern California known as the Coachella Valley.

"The scale of the disaster could be along the lines of Hurricane Katrina," she said. (See complete coverage of Katrina and its aftermath.)

When, Not If

Historical data show that the average time between earthquakes in the southern end of the fault line is 150 to 200 years.

However, the last earthquake struck the area back in 1680.

While scientists can't explain this long gap between seismic activity, the experts are almost certain that it's a question of when, not if, the next one will strike.

"Even though there hasn't been an earthquake in a long time, the reality is that there will be one," explained Tom Fumal, research geologist with the U.S. Geological Survey's Earthquake Hazards Team.