30 Years After The Northridge Quake, What’ve We Learned?

On Jan. 17, 1994 the Northridge earthquake struck Southern California early in the morning. The violent shaking — produced by a previously unknown fault — destroyed buildings, infrastructure and displaced tens of thousands of people. According to the U.S. Geological Survey more than 30 were killed and 7,000 injured.

Northridge caught us off guard, and showed us just how unprepared we were for the breadth of the disaster.

Firemen carry a janitorial worker who was rescued from a collapsed garage at the Northridge Mall.

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Denis Poroy

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AFP

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Given that it’s been so long and another earthquake is always on the way, what’ve we learned about quakes since then?

Scientists from the community here in Southern California quake community shared their thoughts.

We’ve gotten much better at earthquake monitoring

After the quake hit at 4:31 a.m., residents turned to experts for answers.

“Our computers were so old and slow we literally couldn’t get the data from the mainshock for a couple of hours after the event,” said Lucy Jones, seismologist and founder of the Dr. Lucy Jones Center for Science and Society.

The general public wanted to know how big the event was, where it was located and what fault it came from, but they, along with everyone else from first responders to government officials, were left in the dark. Not just because of the lack of computing power, but also because the seismic network was lacking.

“That experience directly spurred major improvements and changes in earthquake monitoring,” said Susan Hough, a geophysicist with the U.S. Geological Survey.

Since Northridge, we’ve substantially grown our seismic monitoring networks.

Now, within minutes after a quake, we’ve got a good idea of its location, size and intensity. All critically important information, especially for those that need to be dispatched to help with the disaster.

We can now warn people quakes are coming

Better preparedness tools have come along as a result of that ever improving seismic network, including the ShakeAlert Earthquake Early Warning System, which is able to warn people of shaking before it gets to them.

“Our goal is to give people several seconds before the heaviest shaking arrives. And a lot of that is dependent on where you're located in relation to the epicenter of the earthquake,” said Robert de Groot, who’s part of the ShakeAlert operations team.

So called soft-story structures, with elevated first floors over open space for cars, fared poorly in the 1994 earthquake.

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Courtesy USGS archive

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The system can detect ground motion from an earthquake in a place like Palm Springs, and send alerts to cell phones in Los Angeles faster than the waves of the temblor can travel through the Earth — letting people know that they need to drop, cover and hold on.

You’ll be alerted of larger quakes via the Wireless Emergency Alert system, which should be enabled on most smartphones. Though, if you’d like to install an app that alerts you of smaller quakes as well, MyShake from UC Berkeley is an option.

One column of the overpass is standing. Cars lie smashed by the collapsed Interstate 5 connector in Sylmar on Jan. 17, 1994.

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Jonathan Nourok

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AFP

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Serious shaking can occur far from the epicenter

While the epicenter of the earthquake was in the San Fernando valley, Santa Monica got hit harder than expected.

“That was because of the focusing of the seismic waves, kind of like waves going through a magnifying glass,” said Elizabeth Cochran, a seismologist with the USGS.

“Underneath the Santa Monica mountains there's really hard rock. As you move into the L.A. basin, there's soft rock. And because of that, the waves kind of bend in certain ways, sometimes bending towards each other such that all of the energy is directed in one location.”

A mother and her children walk near a tent city at Winnetka Recreation Center on Jan. 22, 1994 as the California National Guard sets up the shelters for the thousands of Angelenos made homeless by the quake.

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Tim Clary

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AFP

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We build better buildings (but many are still dangerous)

Structural engineers had a whole lot of takeaways from Northridge, including that the welds used in the construction of some of our tallest steel buildings were weaker than previously understood.

“Fortunately the shaking was not strong enough to cause collapse of high rises, but lots of study done post the earthquake shows that had the earthquake been a magnitude 7-ish, it probably would have caused the collapse of high rise buildings,” said Tom Heaton, professor emeritus of engineering seismology at Caltech.

We’ve significantly overhauled how we construct steel buildings since then, but there are an awful lot of buildings constructed here prior to 1994. I covered this in detail several years ago for The Big One podcast, pointing out the questionable construction underlying two famous buildings in downtown L.A.

Besides steel buildings, we’ve also seen major retrofits required for soft-story apartment buildings (which collapsed in the quake), and non-ductile concrete buildings, all of which are susceptible to big quakes. Many buildings still need to be retrofitted.

Northridge also prompted the reexamination of what we expect from buildings after an earthquake, besides “don’t collapse.”

A resident fills a water jug on Jan. 18, 1994, at one of many water lines set up in the area to assist victims of the Northridge earthquake. Local authorities warned residents not to drink tap water after the quake broke many water mains in the area.

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Chris Wilkins

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AFP

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“Important structures that were necessary to bring the city back to function were yellow tagged or red tagged, and even if they didn't collapse and didn't kill people, they actually put the economy backwards and had to be closed and retrofitted over time,” said Domniki Asimaki, professor of mechanical and civil engineering at Caltech.

“It's not enough for us to build buildings to meet life safety and collapse prevention. It is important for us to build buildings to meet the performance criteria that we set for each building.”

California’s requiring hospitals be retrofitted with the goal that each will remain functional after a quake.

Firefighters cross a street as a broken 16-inch gas main burns in the background, after the Jan. 17, 1994 quake.

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Hal Garb

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AFP via Getty Images

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We need to worry about the small faults too

Northridge was a good reminder that we need to worry about faults besides the giant San Andreas.

“It happened on a smaller fault and it was only a 6.7, but what made it really devastating was its location. There was a fault just right underneath an urban area really close to where a lot of people live,” said Clara Yoon, seismologist with the USGS.

Smaller magnitude quakes located right under a whole bunch of people can do a lot of damage.

I’ve always got my eyes on the Puente Hills fault, which is smaller but scary. It runs under some of the most populated parts of L.A. County and is capable of producing a massive magnitude 7 earthquake.

Oh, and you should remember that even if you look at a fault map and don’t see one near you (which is unlikely), there are a whole bunch of faults that’ve not yet been discovered. That’s exactly what happened with Northridge. We didn’t know the fault existed before the quake occurred, adding to the confusion on the morning of the disaster.

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