LOS ANGELES
-- People across Southern California on Thursday looked like they had stepped out of a disaster movie. Children ducked under their desks. Victims with fake blood lay on the ground. First responders sprang into action to treat the "wounded."

The controlled chaos was all part of a mock "Big One" - an earthquake drill billed as the largest in U.S. history and aimed at testing the preparedness of governments, emergency responders and residents.

At 10 a.m., a cast of millions dropped to the ground, covered their heads and held onto furniture. Local television stations interrupted their regular programming to announce the drill and covered it as they would a major earthquake, though with continual reminders that the emergency wasn't real.

Thursday's drill was based on a fictional magnitude-7.8 event on the southern San Andreas Fault. If such a quake occurred today, scientists estimate it would kill 1,800 people and cause $200 billion in damage. Some high-rises would fall, sections of freeways would crumble and gas pipes would crack.

The dress rehearsal served to remind Californians that they live on shaky ground that can rupture without warning. That southern San Andreas has not popped in more than three centuries, and scientists fear stress buildup could unleash a big quake.

"We're really taking a step forward toward earthquake safety," said Lucy Jones, a U.S. Geological Survey seismologist who has long urged residents to prepare.

At Bishop Alemany High School, a San Fernando Valley campus badly damaged by a 1971 quake and destroyed by the 1994 Northridge disaster, the football field was filled with hundreds of mock mass casualties who wore colored wristbands indicating the severity of their fake injuries.