Two major earthquakes have hit the Bay Area in modern history. In 1906, a 7.9 magnitude earthquake hit San Francisco and 80 percent of the city's buildings fell or burnt to the ground, leaving 300,000 people homeless and killing nearly 3,000. In 1989, a 6.9 magnitude quake caused the ground to liquefy in parts of the city and collapsed highways, killing more than 60 people.

A new report from the U.S. Geological Survey says that there is more than a 70 percent chance that a 6.7 magnitude or higher earthquake will hit the area in the next 30 years.

At the same time, the city is experiencing a building boom and skyrocketing real estate. But the U.S. Geological Survey report also shows that some of the city's skyscrapers may not be seismically sound.

Here's why San Francisco is not as ready as one may think when the next big earthquake hits.



