Although this new suburb of 80,000 people was just a few miles from the epicenter of a 5.4-magnitude earthquake, the city withstood the shaking with almost no damage at all.
If a quake had to hit somewhere in densely populated Southern California, Chino Hills was about the best place possible.
Nearly three-quarters of the city’s residential subdivisions were built in the last 15 years and feature the latest in plywood-reinforced walls, tied-down foundations, strengthened concrete and stronger welds.
Other communities farther from the epicenter of Tuesday’s temblor saw fallen bricks, cracked walls and windows, warped door frames and broken water mains and gas lines.
One big reason: Chino Hills went up mostly in the mid- to late 1990s and was built to the stringent earthquake standards that the state wants to see adopted everywhere across California before the Big One strikes.
“I was wandering around out there after the quake and it struck me that there’s no building there that’s more than 10 years old. They’re all built to the most recent codes, and I think that’s true of the whole Chino area,” said Lucy Jones, a seismologist with the U.S. Geological Survey. “The type of earthquake that used to be a major event just isn’t anymore.”
Since the 1930s, California has gradually boosted its building standards. Each severe quake has prompted new rules, with the most recent major overhaul coming after the 1994 quake in the Northridge section of Los Angeles that killed 72 people.
After that disaster, the building code was amended to require, among other things, the use of plywood to reinforce sheetrock walls in homes. The new rules also prescribed a different way of welding steel that makes the welds less likely to become brittle and crack.
Tuesday’s jolt proved to structural engineers that their work is paying off.
In Chino Hills, 30 miles southeast of Los Angeles, about 70 percent of the homes date to the mid- to late 1990s, and the city doesn’t have a single unreinforced mortar building, said Winston Ward, the city’s chief building official. Most commercial buildings are no more than four stories tall.
Some, including a newly built Hindu temple, have foundations that rest on a type of rubber-and-metal bumper to lessen swaying, he said.
Experts said Tuesday’s quake could have produced more damage if it had been centered elsewhere.
Only about 20 percent of buildings statewide are constructed to the standards used in Chino Hills. Of the remaining 80 percent, 40 percent would suffer major damage during a severe earthquake and 10 percent would collapse, said Chris Poland, chief executive at Degenkolb Engineers in San Francisco. Tuesday’s quake was considered moderate.
A state law passed in 1986 mandated that cities catalog all unreinforced masonry structures — mostly old brick or stone buildings — and then take steps to retrofit them, a process that includes inserting steel reinforcing bars in exterior walls, and bracing the interior walls with steel, too.
But the law left the retrofitting plans to individual jurisdictions. As a result, about 30 percent of the state’s nearly 26,000 brick-and-mortar structures could collapse in a large quake, according to a 2006 report by the California Seismic Safety Commission. Those include buildings with unbraced parapets and unsecured walls and roofs.
Two women were killed in 2003 when an older building collapsed on them during a 6.5-magnitude quake near Paso Robles, along the Central Coast. Following that disaster, cities began posting plaques outside buildings that have not been retrofitted.
In San Bernardino, 40 miles from Chino Hills, there are more than 200 buildings that have not been reinforced because of resistance from business owners, said Jones, the seismologist. Had Tuesday’s quake struck there, the damage could have been much worse.
But retrofitting commercial buildings and high-rises can cost 30 percent to 150 percent of the value of the structure, while upgrading a home can be as much as 30 percent, Poland said.
“When there’s no earthquakes, it’s hard to make anything change,” said Thomas Heaton, a professor of geophysics and engineering at Caltech
Experts nonetheless hope that Tuesday’s quake will prompt cities to take action before the Big One — a quake of 7.8 or more — arrives.
“In the end, it bears fruit, and we can look around and say, “Hey, this stuff actually works,” said Ward, the Chino Hills building chief.
Associated Press Writer Alicia Chang contributed to this report.
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