Southern California seismologist Lucy Jones' job is to study earthquakes for ways to make people safer.
Known as "The Earthquake Lady," Jones spends a lot of time focused on the vast gap between what scientists know about the next big quake's potential impact on the region, and what the region has done to prepare.
Much of the existing knowledge comes from the 6.7 magnitude Northridge earthquake that hit 20 years ago Friday, killing 57 people and causing $20 billion in damage: collapsed buildings and freeway overpasses, snapped water and gas lines, rampant fires and landslides.
The Northridge earthquake was one of the worst natural disasters in the nation's history, an emblem of urban catastrophe. But it also provided researchers with loads of information to help make the Los Angeles area more resilient.
The problem is that "very little has changed," Jones said.
This persisting vulnerability, ranging from obsolete architecture to public complacency, remains among the most troublesome aspects of the Northridge earthquake legacy.
Here are five top unresolved concerns:
1. The Northridge Earthquake was bad, but the next "big one" could be much worse.
In some respects, Los Angeles got lucky with Northridge. It occurred at 4:31 a.m. on a relatively short, unknown fault, and the brunt of its force was concentrated in less densely populated and outlying areas of the city. If it was stronger, and had spread through a more crowded, widespread area at a different time of day, the toll likely would have been much higher.
A few weeks ago, Jones gave a lecture to the American Geophysical Union called "Imagine America Without Los Angeles," in which she outlined what would happen if an 8.0-magnitude quake struck along the San Andreas fault. This "big one" could decimate the local economy, mostly because businesses wouldn't be able to reopen, people wouldn't be able to get to work, and communication systems wouldn't operate. Under that scenario, many residents would flee for other parts of the country, leaving Los Angeles a much smaller city.
"Northridge was not a big quake," Jones said in a recent interview. "It was bad, but it was only a 10-mile-long fault, and it was a 6.7. It wasn't under the city, but the suburbs. If we had the same quake on another fault, we'd have way more damage."
The U. S. Geological Survey has estimated that such a quake could directly affect 10 million people, about 20 times the number of Northridge.
"Southern Californians may not be so lucky in the next event," the USGS said in a post-Northridge analysis. "Another earthquake of similar magnitude could focus the strong shaking directly at a densely populated region, or the next earthquake could simply be larger with damage spread over a much greater area."
2. Thousands of Southern California's buildings remain at risk of collapse.
After every major earthquake, authorities examine how the region's construction held up, and decide what needs to be improved. Northridge was no exception.
But that doesn't mean that all the weaknesses have been corrected.
The 1994 quake's worst building collapse was at the Northridge Meadows apartments, where 16 people were crushed. The complex was a "soft story" structure, with open-air parking on the ground floor and dwellings above. Thousands of these buildings, supported by narrow columns and considered one of the most vulnerable construction types (along with brick and concrete), remain scattered around the region.
Also during Northridge, the steel frames of many buildings cracked. The failure surprised engineers, who thought the steel to be earthquake resistant. Many of those buildings have since been repaired, but no one knows exactly how many others remain damaged.
Some homes that were not bolted to their foundations slid off during the Northridge quake. Many similarly built homes remain at risk of doing the same during the next one.
Pre-1970s concrete buildings, including some of the city's tallest structures, lack steel reinforcement bars that could keep them from collapsing in a big earthquake. An analysis by the Los Angeles Times found more than 1,000 old concrete buildings at risk of collapse, and 50 that could be destroyed, "exposing thousands to injury or death."
These post-Northridge findings led to updates to the building code, a quest for engineering solutions, and calls for retrofitting.
The efforts echoed changes made in response to earlier earthquakes that exposed brick (or "unreinforced masonry") buildings as collapse-prone. The city passed a mandatory law to retrofit such buildings. As a result, no one died in collapses of such buildings during Northridge.
"That shows that at least in these areas we're paying attention to, with resistance and building codes, we're on the right track," said Jim Harris, an expert in earthquake engineering and president of J R Harris & Co., a structural engineering firm in Denver.
The Los Angeles City Council recently agreed to seek funding for building officials to inventory structures with designs similar to those that gave way during Northridge and in prior quakes.
But there is no universal mandate for retrofitting buildings, and oversight of individual retrofit projects remain spotty. Officials have balked at forcing property owners to make safety improvements. Attempts to create a public list of vulnerable buildings have failed.
"Tens of thousands of bad buildings are still out there," Jones said.
3. Not enough homeowners have earthquake insurance.
One of the most profound economic consequences of the Northridge earthquake was the near-devastation of the housing insurance market. Twenty years later, it has yet to fully recover.
Prior to Northridge, the state's home-insurance companies were required to offer earthquake coverage. Their policies, it turned out, drastically underestimated losses that would result in even a moderate quake.
When Northridge hit, homeowners filed $12.5 billion in claims, nearly wiping the insurers out. The following year, most of the companies backed out of the homeowners market or stripped their policies to the bones.
The ensuing crisis threatened to bring down the real estate market. That forced lawmakers to create the California Earthquake Authority, a state-run insurance pool.
Even so, fewer California homeowners have earthquake insurance today than when Northridge hit, said Glenn Pomeroy, the authority's CEO. Only 11 percent of people who have homeowners insurance have earthquake policies, down from as much as 30 percent two decades ago.
"It's not a rosy picture," he said.
Why? First, cost. The authority uses modern data to predict earthquakes, which means that many areas presumed relatively safe are in fact at greater risk. That has made the authority's coverage a lot more expensive.
Also, many people have gone so long without experiencing a serious quake that they no longer think about the risk, Pomeroy said. Some assume that they'll get bailed out by the federal government if they lose their homes. A smaller number don't realize that their existing homeowner's policy does not include earthquake coverage.
The authority is trying to urge more Californians to consider earthquake insurance, while pushing Congress to approve legislation that would provide the authority with financial assistance to cut rates.
"We do know that the next big one is coming. We just don't know when," Pomeroy said.
4. The water system could fail again.
During Northridge, much of the region's aging water system broke down, cutting water pressure to homes and making it difficult to fight fires. Most of the pipes, which fracture frequently during normal circumstances, have not been upgraded.
That, Jones said, means that a failure during a large earthquake could be calamitous.
A USGS report estimated that it could take six months for the system to return to normal after a major earthquake.
"The DWP (Los Angeles Department of Water and Power) is working at trying to figure out how to change this," Jones said. That includes working with scientists developing quake-resistant pipes, she said.
This is not only a firefighting concern, but an economic one. If it takes six months to get water restored, that means countless businesses could be shuttered, Jones said. Not to mention the similar challenges of failed electric and telecommunication systems.
5. Most of us are not prepared.
In 2010, a study commissioned by the California Emergency Management Agency found that fewer than 20 percent of households have reinforced their homes or had them inspected for earthquake resistance. Only 40 percent had made family disaster plans.
A similar proportion stored the minimum recommendation of three gallons of water per person. Even in the highest-risk areas, people were not as prepared as they ought to have been.
"Those are numbers we definitely have to improve upon," Greg Renick, a spokesman for the state Office of Emergency Services, said recently.
The findings triggered a public education campaign that continues today. The culmination, every October, is the "Great Shakeout," a drill that has grown to involve more than 5 million people.
Officials and scientists are working to implement state-of-the-art earthquake monitoring systems. And Gov. Jerry Brown has directed state officials to pursue the development of an early-warning system, Renick said.
One of the biggest obstacles in the public education campaign is human nature, researchers say.
Those who remember surviving a bad quake are more apt to take the threat seriously. They are also more likely to experience post-traumatic stress symptoms when the next one hits.
But a bad one hasn't happened in a while. So that memory is fading.
The key is preparation, said Roxane Cohen Silver, a professor of psychology and social behavior at the University of California at Irvine who has studied what makes some people more resilient after surviving a natural disaster.
"We do believe that having prepared to some degree with supplies and a plan does assist people in the aftermath because there is a sense of having worked through what to do next," Silver said.