The quake, which rocked the region from Los Angeles to San Diego on Tuesday, caused only limited damage and minor injuries, and served as a reminder of the seismic danger below sprawling freeways and subdivisions.
Homes and businesses reported widespread but minor damage such as fallen ceiling tiles, cracked walls and windows and warped door frames.
The temblor's epicenter was located just outside Chino Hills, 29 miles southeast of downtown Los Angeles in San Bernardino County, and it was felt as far east as Las Vegas. At least 90 aftershocks followed as of Wednesday morning, the largest a magnitude-3.8 that came about 10 minutes after the main quake.
"We were really fortunate this time," said Capt. Jeremy Ault of the Chino Valley Independent Fire District. "It's a good opportunity to remember that we live in earthquake country. This is part of living in Southern California and we need to make sure we're prepared."
Dr. Lucy Jones, a government seismologist, recently ran a first-of-its-kind model predicting what would happen if a 7.8 magnitude earthquake hit southern California - that's 10,000 times the energy of Tuesday's quake, reports CBS News correspondent Ben Tracy.
The government estimates 1,800 people would die, 50,000 injured and there would be $200 billion in damage, Tracy reports.
"We are not nearly as prepared as we should be if the big one were starting right now," Dr. Jones said.
Chino Hills was incorporated in 1991, so much of the construction is newer and built to modern safety standards, city spokeswoman Denise Cattern said. There were no reports of harm in the city of 80,000, she said.
"We have all the latest building standards and that probably made a difference," she said.
Cell phone providers, however, were overwhelmed by the event. Cattern said public works employees in the field had to find land lines to call headquarters because their cell phones wouldn't work.
Sprint Nextel Corp. reported a spike of 800 percent right after the quake and Verizon Wireless saw the volume jump by 400 percent over that of a typical day. It wasn't clear how long the systems were overloaded but they were back to normal Wednesday.
"The demand was just incredible," Verizon spokesman Ken Muche said in Orange County.
Volume was about 40 percent higher than Verizon had projected would occur in a disaster, Muche said Wednesday.
"Whether it's a freeway or cell network, no network has infinite capacity," he said. "There were so many calls happening at the same time."
The magnitude-5.9 Whittier Narrows quake in 1987 was the last big shake centered in the region. Scientists were trying to determine which fault ruptured Tuesday, but they believe it is part of the same system of faults. The 1987 earthquake heavily damaged older buildings and houses in communities east of Los Angeles.
As strongly as it was felt, Tuesday's quake was far less powerful than the deadly magnitude-6.7 Northridge earthquake that toppled bridges and buildings in 1994. That was the last damaging temblor in Southern California, though not the biggest. A 7.1 quake struck the desert in 1999.
Derek Black, a 19-year-old personal trainer, said it was the first large earthquake he remembered despite living in the area since birth.
Black said he was helping a client do pull-downs when the floor started to rumble. He grabbed onto a weight machine and turned toward the wall, which was covered in floor-to-ceiling mirrors.
"The mirrors were rippling all the way down," he said. "Seeing it in the mirrors was what made me realize, `Geez, this is huge."'
The heaviest shaking was northwest of the epicenter near suburban Diamond Bar, said Thomas Heaton, director of the earthquake engineering and research laboratory at Caltech. He said all buildings constructed in the region since the 1930s should withstand the kind of shaking felt Tuesday.
The earthquake had about 1 percent of the energy of the Northridge quake, he said.
"People have forgotten, I think, what earthquakes feel like," said Kate Hutton, a seismologist at Caltech. "So I think we should probably look at it as an earthquake drill."
The state Office of Emergency Services in Sacramento received scattered reports of minor infrastructure damage, including broken water mains and gas lines.
"I thank God there have not been any reports of serious injuries or damage to properties," Gov. Arnold Schwarzenegger told a televised press conference. "People understandably are very nervous."
Minor structural damage was reported throughout Los Angeles, along with five minor injuries and people stuck in elevators, said City Councilwoman Wendy Greuel, serving as acting mayor. She said there was flooding in one department store.
The jolt caused a fire but no injuries at a Southern California Edison electrical substation in La Habra, about 12 miles southwest of the epicenter, spokesman Paul Klein said. Damage there and to other equipment led to some power outages in Chino Hills, Chino, Diamond Bar and Pomona, he said.
To prepare for the "Big One," scientists and emergency planners in the fall will hold what is billed as the largest earthquake drill in the country. It will be based on a hypothetical magnitude-7.8 temblor. Earlier this year, scientists calculated that California faces a 99.7 percent chance of a magnitude-6.7 quake or larger in the next 30 years.