Thursday will bring the state's latest Great Shakeout drill, which is designed to remind Californians what to do when the next large quake strikes.
Nearly 944,000 individuals, schools, government agencies, cultural institutions, hotels and other businesses in San Diego County are scheduled to participate, according to event organizers. The total in California is over 10.4 million.
Shakeout organizers said most San Diegans live within 15 miles of a fault, including the Rose Canyon fault, which runs beneath downtown and along the coast.
Local experts believe a major breach of Rose Canyon could cause considerable damage, but it hasn't produced a large shaker since before Europeans settled the area.
Two more faults, the Elsinore and San Jacinto, cut through East County.
San Diego is also prone to feeling major earthquakes that occur elsewhere, including the magnitude-7.2 temblor on Easter Sunday 2010 that was centered south of Mexicali, and the 7.3 Landers quake in 1992 that took place in the Mojave Desert.
If a major temblor struck, officials said those affected should look for the nearest, safest place to take cover -- like under a sturdy table or desk - - and protect their heads from falling items or breaking glass. An interior wall away from windows, overhead fixtures, wall hangings or furniture that could topple over may also suffice until the shaking stops.
County officials noted that building collapses are not likely in San Diego County, so running outside is not the safest option. While running, a person could be hit by falling electrical lines, tree branches or building facades.
People already outside when a quake strikes should move away from buildings, trees and overhead power lines, then to drop and cover their heads.