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By Dan Whitcomb
LOS ANGELES, July 29 (Reuters) - An earthquake struck just east of Los Angeles on Tuesday, rocking tall buildings and rattling nerves across Southern California, but causing no serious injuries or major structural damage.
The quake hit at 11:42 a.m. local time (1842 GMT) about 30 miles (48 km) east of Los Angeles in suburban Chino Hills and registered magnitude 5.4 -- making it the strongest seismic event centered near America's second-largest city since the 6.7-magnitude Northridge quake in 1994.
It was followed in the next few hours by more than two dozen aftershocks, the largest measuring 3.6, and geologists said there was a small chance it could be a foreshock to a larger earthquake still to come.
"I think we were very lucky with this one," Gov. Arnold Schwarzenegger told a news conference in Sacramento, adding he called his Los Angeles-area home to speak with his wife, Maria Shriver, immediately after the quake.
Magnitude 5 quakes are considered moderate but are still capable of causing damage. The U.S. Geological Survey said Tuesday's quake was shallow, about 8.5 miles (13.6 km) deep.
Across Southern California, the temblor was felt as a strong jolt, swaying tall buildings in downtown Los Angeles and Orange County and sending office workers into the streets.
"I immediately went and stood under a doorway," said Rachel Feldman, a 27-year-old attorney who works in the 75-story US Bank Tower in downtown Los Angeles, the tallest building in the western United States.
Sara Phillips, 28, also an attorney in the US Bank Tower, said: "I wasn't scared. The building is on rollers so it made me feel like I was going to barf."
Elsewhere, water mains broke and goods fell off store shelves but no serious injuries were reported. Airports, ports, power grids and nearby nuclear power plants all reported no structural damage or interruption in service.
The ground shook for hundreds of miles km and was felt as far south as the Mexican border and east to Las Vegas and Flagstaff, Arizona.
In Chino Hills, where the shallow quake struck some 7 miles (12 km) below the surface, spokeswoman Denise Cattern said no reports of damage of injury were reported in the city of 80,000 but that residents were unnerved.
"Most people agreed it was the biggest earthquake they ever felt," she said.
James Destefano, city manager in neighboring Diamond Bar, said pictures and cabinets fell at City Hall.
"We experienced the same effects as everyone in this immediate area," he said. "We were rocking and rolling for about 15 to 20 seconds."
A spokesman for the San Bernardino County Sheriff's Office said there were no reports of injuries, although several water mains broke in the area, flooding streets.
The Northridge quake, which struck just before dawn on Jan. 17, 1994, killed 57 people, collapsed an apartment building and caused billions of dollars in damage. City officials have since strengthened building codes for new construction and required retrofitting of older buildings.
"In California, fortunately because of our good building standards, we would not expect to see structural damage with a (magnitude) 5.4," said Kate Hutton, seismologist at the California Institute of Technology, or Caltech.
Caltech and USGS experts estimated that Tuesday's quake released only 1 percent of the energy unleashed by the 1994 disaster.
But they noted there was a 5 percent chance the Chino Hills quake was a foreshock to a larger seismic event.
"I think we are as prepared as anyone can be. I think we're better prepared than any other state for emergencies like that," Schwarzenegger said. "After (Hurricane) Katrina, what happened there, made us really re-evaluate everything."
In Anaheim, 40 miles (64 km) south of L.A., workers at Disneyland removed visitors from rides but the world-famous amusement park remained open and rides were resuming.
The quake did not hinder operations on the state's power grid or damage California's two nuclear plants, utility and state officials said.
Phone service remained operational but AT&T reported a sharp spike in calls that left customers with busy signals.
Los Angeles is the most populous city in California and the second-most populous urban area in the United States. According to 2000 Census Bureau figures, about 3.6 million people live in the city of Los Angeles, while Southern California is home to more than 20 million people. (Additional reporting by Bernard Woodall, Deena Beasley, Lisa Baertlein, Alex Dobuzinskis, Jennifer Martinez, Syantani Chatterjee and Nichola Groom in Los Angeles and Alexandria Sage in San Francisco; Editing by Mary Milliken and Peter Cooney)