Dozens of schoolchildren took shelter Thursday under work tables along with scientists and government officials as California practiced how to survive a major earthquake.
The scene at the California Science Center was to be repeated throughout the state, with millions of participants in offices, schools and emergency agencies.
The fourth-graders who participated in the drill in Los Angeles had been chanting "drop, cover and hold," moments before the simulated earthquake was announced.
Some 6.7 million Californians signed up to take part in the earthquake disaster drill, billed as the largest such exercise in U.S. history.
Many schools and businesses were to practice "drop, cover and hold on" — the minimum requirement for participation. Some hospitals and fire departments planned more elaborate simulations complete with search-and-rescue missions and people posing as faux quake victims.
Last year, the state held its first large-scale quake preparedness drill, focusing on Southern California. Some 5.5 million around the region participated, from school children ducking under their desks to firefighters doing medical triage.
After last year's drill, organized decided to hold one every year.
Loma Prieta anniversary
This year's exercise occurs during the same week as the 20th anniversary of the Loma Prieta earthquake that killed 63 people, collapsed a major freeway, and caused nearly $6 billion in damage around San Francisco Bay. The magnitude-6.9 temblor struck before the start of the third game of the 1989 World Series.
California, one of the most seismically active states in the United States, faces a 46 percent chance of being hit by a 7.5 or larger earthquake in the next 30 years, according to the U.S. Geological Survey.
The last temblor to cause significant damage in California was the 1994 Northridge disaster.
The drill is sponsored by the Earthquake Country Alliance, made of up USGS, state Emergency Management Agency, American Red Cross and others.