"More than 24 million people, including 9 ½ million in California, have signed up to duck under their desks at 10:17 a.m. local time Thursday, cover their heads and hold on to something sturdy.

The exercise allows first responders to dust off their emergency response plans and transportation departments to practice slowing down trains in the event of real shaking.

The Great ShakeOut was first held in California in 2008 and participation has since spread around the globe. This year, Japan, Canada, Italy and Guam planned to join the U.S. in the drill.

"Everyone everywhere should know how to protect themselves during an earthquake," lead organizer Mark Benthien said."