The 4:31 a.m. jolt hit Los Angeles from 11 miles deep, shaking it from its slumber with a temblor that would topple freeways, ignite fires and inflict $49 billion in overall damage to homes and businesses, killing dozens of Angelenos.

Yet the 6.7-magnitude earthquake that hammered the San Fernando Valley 20 years ago this week wasn’t even the dreaded Big One.

“My wife was pregnant. I thought I got kicked out of bed because I was snoring,” said George McQuade, of West Hills, who then lived in a condominium in Reseda. “I was literally thrown to the floor.

“My wife and I looked at each other and said, ‘Earthquake!’”

The 1994 Northridge Earthquake on Jan. 17 ripped across the region and rattled 10 million Angelenos in what would be the costliest temblor in U.S. history. For roughly 10 horrifying seconds, the Southland shuddered into widespread urban collapse and chaos. It took years to rebuild from the nation’s first earthquake that struck from directly beneath a metropolitan area.

Sleepers were hurled from their beds. TVs, shelves and chandeliers tumbled in a cascade of debris. Homes and businesses were splintered from Fillmore to Santa Monica and beyond. The shaking ground was felt from Las Vegas to San Diego.

Peppered by powerful aftershocks, parts of the city were left in ruins within minutes. Businesses crumbled. Parking garages collapsed. Homes fell. Fires raged. A 64-car Southern Pacific freight train derailed, spewing a cloud of sulfuric acid.

Steel building frames designed to resist earthquakes cracked, while reinforced concrete columns crumpled.

Amid the jumble of shattered windows, chimneys and earthquake debris, nine wrecked hospitals became unusable, schools and universities unworkable, roads strewn with power lines undriveable. Seven major freeway bridges collapsed, stranding early morning commuters on soaring precipices. Close to 200 bridges were damaged.

Power, telephone and water service died.

A giant cloud rose above a lightless city, broken only by the glow of nearly 800 reported fires, according to Los Angeles fire officials.

“I never saw a blacker sky,” recalled Susan Massarik Aslan, 52, of Somas, who wrote a memoir of how her 5,000-square-foot Granada Hills dream home was destroyed. “There was no electricity in our city. No twinkling of distant lights. Then all of a sudden, as if the sun rose, the sky lit up in hues of orange and red. But it wasn’t the sun; it was a fiery explosion blocks away (on Balboa Boulevard).”

Among the wreckage were some 90,000 destroyed or damaged homes, offices and public buildings, according to the state Office of Emergency Services, with 48,500 homes cut off from water and roughly 20,000 without gas. Some 125,000 residents were rendered temporarily homeless.

When the dust settled, 57 people had died — including 33 from fallen buildings. Of those, 16 were killed when the 164-unit Northridge Meadows apartments collapsed atop its downstairs parking garage.

The fatalities included Los Angeles Police Officer Clarence Wayne Dean, whose police motorcycle plunged 40 feet off a collapsed section of the Antelope Valley Freeway. The Highway 14/Interstate 5 interchange was later renamed in his honor.

More than 9,000 people were injured, including hundreds treated outside a topsy-turvy Northridge Hospital Medical Center. Twenty-one preemies from its neonatal ICU were airlifted to other hospitals.

If not for the early hour, the federal Martin Luther King holiday and upgraded building standards since the 1971 Sylmar quake, some say the carnage could have been much worse.

Among the rubble were Pic ’N’ Save stores across the region, four of which were forced to close, including a Simi Valley store whose roof had completely caved in.

“Everything fell off the shelves,” said Chuck Warnicke, 70, of El Monte, a former fixture installer for the retail chain later bought by Big Lots. “You couldn’t walk. The ceiling tiles fell down. The lights fell down. It was bad.”

Within a day, Los Angeles firefighters managed to snuff out hundreds of blazes, despite faulty radios and no water pressure because of broken mains. Nine L.A. police officers would be decorated for forming a human chain to rescue a woman and her dog buried in a collapsed hillside home in Studio City. L.A. Department of Water and Power workers went without sleep for days to restore power.

A costly quake

The quake cost $20 billion in property damage — the most expensive U.S. natural disaster until Hurricane Katrina’s $81 billion toll on New Orleans in 2005 — plus $29 billion in economic losses. It would far exceed the combined cost of 50 years of earthquakes, windstorms, wildfires, floods and landslides across Los Angeles County, according to a NASA Jet Propulsion Laboratory study.

The response from the Federal Emergency Management Agency, which would pour $14 billion into the region, was immediate. As a result of FEMA aid, California State Northridge would fix 107 buildings damaged or destroyed by the quake.

More than 681,000 residents and businesses applied for federal disaster aid, a state record, according to the OES.

“It was a wake-up call,” said JPL Climatologist Bill Patzert, author of the report. “If you add up the costs of all of our natural disasters, it’s pocket change compared to the Northridge Quake. The impact was so large, people are still trying to get their arms around it 20 years later.”

At an earthquake summit at the California Institute of Technology recently, seismologists highlighted how, two decades later, the scientific and technological ground had shifted.

“Northridge revolutionized the field,” said Southern California earthquake expert Lucy Jones, science adviser for risk reduction with the U.S. Geological Survey, in Pasadena. “Because of Northridge, we focus a lot of energy on what goes on in the Los Angeles Basin. We literally built a CT-scan of Los Angeles and the San Fernando Valley to get a picture of what the faults were.”

Despite its name, the Northridge Quake sprang from an unknown fault 11 miles beneath what was actually Reseda, geologists say. The blind thrust fault angled upward toward Chatsworth, with no tell-tale signs on the ground above.

When the 10-mile fault slipped, it ruptured for seven seconds, ripping two planes of rock past each other an average 10 feet — cranking out some of the strongest ground motions ever instrumentally recorded in a large North American city, with a peak ground acceleration of 1.8 g shooting south into Tarzana.

It took scientists 45 minutes to determine its 6.7-magnitude energy — a process that would now take two minutes with today’s digital high-tech sensors. Since the earthquake, scientists have built a digital seismic monitoring network that can create detailed models, or Shakemaps, of widespread earthquake intensity in order to aid responders. The system is so successful it’s now being used nationwide.

They’ve now mapped an entire network of previously unknown faults lurking beneath Greater Los Angeles, including the Puente Hills fault beneath East L.A. Seismologists say the fault, if it should ever rupture, could cause a 7.2-magnitude or greater earthquake directly beneath downtown.

“This would be the earthquake from hell, because it’s right beneath Los Angeles,” said Tom Jordan, director of the Southern California Earthquake Center at the University of Southern California.

An even worse earthquake — the “Big One” — would be a major temblor along a 200-mile stretch of the San Andreas Fault that could devastate Southern California, according to models created as a result of Northridge. A magnitude-7.8 earthquake based in Palm Springs would soon overwhelm Los Angeles, forecasters say, sparking 1,600 fires, damaging 300,000 buildings and causing $213 billion in economic losses. As many as 1,800 residents would lie dead among the rubble, and 50,000 more would suffer serious injuries.

The catastrophic forecast has helped spawn Great ShakeOut earthquake drills for millions of Californians. An early warning system may also be within scientific reach.

Problems remain, experts say. Despite decades of seismic retrofitting and building code upgrades, many apartment and concrete buildings may be at risk, while city fault maps may not be up to date. Los Angeles has ordered surveys of soft-story apartments, like the former Northridge Meadows, as well as brittle concrete buildings that could crumble during a quake.

Another urban quake like Northridge could also cripple Los Angeles ports, the U.S. lifeline for goods from Asia. Twenty years after Northridge, Los Angeles depends on cellphone systems with hundreds of towers untested by a major temblor. And the Internet which, should it go down, could disrupt the entire economy.

“Northridge was a significant earthquake to Southern California, but it was not the Big One,” said Mark Benthien, spokesman for the earthquake center. “Prepare like you’re going camping for three days … and don’t expect any help for up to a week.”

Anyone old enough to remember the 1994 Northridge Earthquake can relive it with slow-motion recall. The violence. The ruin. The wailing children in adjacent rooms.

After the earthquake, Susan Aslan and her husband Ken lived with their two children inside a driveway motor home for six months. It took seven years for them to rebuild their home from the frame up — themselves. Their neighborhood was devastated, with homeowners fighting with insurance companies and crooked contractors. One neighbor shot himself after rolling himself up in a rug.

“Finally, it’s just a memory,” said Susan Aslan, a Los Angeles elementary school teacher. “Living through Northridge changed our outlook on life … life is what’s precious. Material things, even if they can’t be replaced, they’re just stuff.”

After the earthquake, George McQuade and his wife, Aida, and their young son had to break out of their third-story Reseda condo, whose doors had jammed shut; the complex’s elevator and corner building had collapsed and were later red-tagged by inspectors. The three of them then camped out for a week at a friend’s apartment in Simi Valley. Like many residents embroiled in repair battles, they let the condo go to foreclosure.

“We think about it every day,” said McQuade, a spokesman for a public advocate for the homeless. “Whenever the house shakes, you get that memory of, ‘Oh my God, here we go again!’ It’s traumatic.

“And unless you go through it, you don’t realize its deadly potential.”