Millions of people plan to drop, cover and hold on in a drill to prepare communities in California and elsewhere for the next big earthquake.
Organizers say more than 10 million Californians registered to participate in the drill at 10:16 a.m. PDT Thursday, in addition to another 15 million people this year in other states and countries.
Schools and universities account for more than half of the participants in this year's Great ShakeOut. A full-scale exercise for emergency responders to prepare for a potential magnitude-6.7 earthquake is planned for Biola University in La Mirada.
The suburb southeast of Los Angeles was rattled by a magnitude-5.1 earthquake in March.
The annual drill began in 2008 in California. It has since spread to dozens of states and countries, including Italy and Canada.