The Great Southern California ShakeOut scenario, visualized in 2008, as based on a potential magnitude 7.8 earthquake along the southern San Andreas Fault, south of Los Angeles. This animation illustrates the speed and impact of such a massive earthquake as it hits Southern California. The potential for this or a similar scenario to actually happen is real and possible in our lifetime.
...and another scenario:
A magnitude 8.0 earthquake erupts along the San Andreas Fault to the north of Los Angeles.