Los Angeles (CNN) -- Twenty years ago, southern California experienced a "big one."
A 6.7-magnitude temblor waylaid Los Angeles on January 17, 1994. Called the Northridge Earthquake, it now stands as the second costliest disaster in U.S. history, after Hurricane Katrina, according to AccuWeather. Northridge cost $42 billion in total damages, while Katrina cost $81 billion, AccuWeather.com said, citing federal figures.
The quake killed 57 people, injured thousands more, damaged 112,000 structures and left more than $20 billion in property losses. More than 20,000 people were displaced from their homes.
The jolt hit Los Angeles' San Fernando Valley at 4:30 a.m. on a Monday, the Martin Luther King Jr. holiday. Had the quake struck on a work day, the toll would have been greater.
Here are a few things we've learned about one of the most studied geological events.
New faults discovered
We all know of California's famous San Andreas fault, but there are other hidden faults.
In fact, the Northridge quake occurred on a fault that no one knew existed. It's called a "blind thrust fault."
Since then, many more faults have been discovered, including one under downtown Los Angeles. If a quake ever stirred there, it could evoke the 1974 disaster film "Earthquake."
"If an earthquake would occur under there, it would be as large as magnitude 7 or perhaps as large as 7.5 and would be extremely destructive," said Thomas Jordan, director of the Southern California Earthquake Center.
Technology's come a long way, baby
At the time of the Northridge quake, there were only three global positioning system stations in southern California measuring the movements of the Earth's plates.
After the quake, NASA led several agencies in creating more than 250 GPS stations as part of the Southern California Integrated GPS Network.
Scientists can now better map fault motions and the probability of future quakes. And researchers are better able to provide instantaneous information about quake locations and intensity.
There has been a big leap in technology since the Northridge quake.
"You have significantly more computing power in the smartphone in your pocket now than we had in all of the computers in the seismolab in 1994," said seismologist Lucile Jones of the U.S. Geological Survey and a visiting research associate at the Seismological Laboratory at Caltech.
Out of the wreckage, a hero and love story
The quake awakened Mike Kubeisy in his third-floor flat in the Northridge Meadows Apartments, which collapsed, killing 16 people, including six of his friends.
As aftershocks roiled the land, Kubeisy began saving lives and pulled people out of the wreckage.
He coaxed one shell-shocked woman named Trish in Apartment 341 down a flimsy ladder, step by step.
In all, he saved five lives. Then-President Bill Clinton later paid him a visit.
"The President of the United States shakes your hand, looks you in the eyes, says 'America is proud of you and you're a hero.' I wasn't ready for that," Kubeisy said. "That's not me. That's all our soldiers. That's our policemen, our firemen. That's not me. I'm a knucklehead. I was just helping our neighbors out."
Still, the day changed his life -- "in hindsight, only for the better," he added.
He ended up marrying Trish in Apartment 341.
Today, they have two sons, now teenagers.
"A lot of friends say the Lord shook the Earth to get you two together," Kubeisy said.
Added son Garrett: "It's just weird to think that something catastrophic would create us. It's just unbelievable when you think about it."
A child is born
Peggy O'Donoghue gave birth in the chaos that immediately followed the quake.
Most people in the nation's second-largest city were asleep at the time of the temblor.
Not O'Donoghue. She was awake counting contractions. She was already eight days overdue.
After the quake hit, she and her husband, Tom, maneuvered through the broken glass of their home and drove their car through an apocalyptic scene: flames spewing from broken gas lines, water flooding streets, and a blackout enveloping the city.
At the hospital, they found shelter in a storage room rocking with aftershocks.
Then a doctor told them they must evacuate: the hospital was unsafe.
After an hour of searching for another medical center, they arrived at Northridge Hospital.
But there were no more beds. Exhausted, Peggy O'Donoghue didn't care. She would deliver her baby on the floor.
But her doctor found a gurney and a room.
More than four hours after the quake hit, Peggy and Tom O'Donoghue had a baby.
They named their son Ryan. But his nickname became Rocky. Or sometimes Shakey.
An hour after the birth, the new parents had to leave again: the hospital needed the bed. Mom, dad and baby drove to her parents' home, where they sat in chairs in the driveway for hours, too afraid to go inside the damaged house because of aftershocks.
Eventually, they found refuge.
Today, Ryan O'Donoghue is awestruck by his parents' resourcefulness.
"Just going through an earthquake in itself is insane, but then having to go through childbirth doing it, it has to be absolutely mind-blowing," Ryan O'Donoghue said. "I say I shook up the world a little bit."
The worst is yet to come
Yes, everyone in California wonders when "The Big One" will strike and create a new beach line.
In fact, the San Andreas fault -- deemed "the 'master' fault of an intricate fault network," the USGS says -- is now due for its once-every-150-years quake. The last big quake on the southern San Andreas occurred in 1857.
"It would be like having a Northridge here and Northridge here and Northridge here," said seismologist Kate Hutton of Caltech, pointing to what the next big one could do to swaths of a California map. "It covers such a wide area that it would be ... a major disaster for the nation."
When "The Big One" strikes
Don't count on the Federal Emergency Management Agency, one expert says.
"FEMA, the government, first responders all tell us they're not gonna be there for the first three days or longer. You need to be able to take care of yourself," said Jeff Primes, president of Ready America Inc., which sells disaster preparedness kits.
So, California, keep a survival kit at home.
And do what experts taught us in school: drop, cover, and hold on.
CNN's Casey Wian, Kyung Lah, Stephanie Elam and Michael Cary contributed to this report.