Hundreds of thousands of San Diegans will take part in the Great California ShakeOut earthquake drill today. Organizers say more than 674,000 San Diego County residents have registered for the event, in which they will be asked to drop, cover and hold on at 10:20 a.m. They’re among a record 8.4 million Californians expected to participate. Earthquake experts say most injuries are caused by falling debris. In the Dec. 22, 2003, temblor near San Simeon in Central California, the two fatalities involved people who ran outside their store, only to be struck by the roof and clock tower of a collapsing building next door. Emergency officials say people indoors when a quake strikes should remain indoors, drop to the floor immediately, get under a sturdy table or desk and hold on to it until the shaking stops. If there are no desks or tables available, they should sit down next to an interior wall away from any windows, mirrors, furniture or fixtures that may fall over. Officials say that trying to run outside or taking a position in an interior doorway are dangerous. The ShakeOut is intended to simulate the impact of a magnitude-7.8 earthquake originating from the southernmost area of the San Andreas Fault. Under this scenario, a tectonic shift would produce waves of movement for hundreds of miles over four minutes. According to the U.S. Geological Survey, some 2,000 people would die, tens of thousands would be injured and more than $200 billion in damage would result from the catastrophe, which would have 50 times the intensity of the Jan. 17, 1994, Northridge earthquake. Hundreds of aftershocks would follow, a few of them nearly as big as the original event, according to the USGS. Californians should be prepared to be self-sufficient for 72 hours following an earthquake or other major disaster. That includes having a first- aid kit, medications, food and enough water for each member of a household to drink one gallon per day for at least 72 hours, according to local and state officials. Homeowners and renters should also know how to turn off the gas in their residences in case of leaks.