This summer’s 5.4 earthquake in Chino Hills showed builders how far seismic safety designs have come in protecting property and lives.
But engineering firms say there is still a lot to learn after each of these quakes.
“There’s a constant evolution of building codes,” said Masoud Bokai, chief executive and cofounder of Irvine-based Borm Inc., a structural engineer.
That’s what happened after the 1994 Northridge earthquake, which led to more than 12,000 injured and $12.5 billion in damages in Los Angeles. That earthquake measured 6.7 on the Richter scale and was one of the most destructive in the state’s history.
In response, building codes were tightened to better protect new structures in the event of an earthquake.
Adding better protection at the joints of buildings was one of the key changes made in the codes, according to Maria Feng, a professor of civil engineering at University of California, Irvine.
July’s relatively minor quake caused some cracking in buildings in Seal Beach, but caused more severe damage in older buildings in Pomona, which was 30 miles from the epicenter, Bokai said.
Orange County is lucky to be located away from a major fault line.
The most significant fault line in the county is off the coast of Newport Beach, which poses less of a threat than major fault lines like the San Andreas, which stretches 800 miles through the state.
Buildings are more secure the farther they are from fault lines, Bokai said.
One technique to protect buildings from earthquakes is to have them built on large rollers that will allow movement with the quake, rather than being held tight, which makes the buildings more vulnerable to breakage.
But due to higher costs for adding this feature, which can tack on more than 10% to a project’s price tag, rollers tend to be used only for critical buildings like hospitals or some high-rises.
Boeing Co.’s Seal Beach facility is an exception after the company retrofitted it with rollers to protect the sensitive work conducted there, according to George Richards, president and cofounder of Borm.
Some have been pushing to adopt a single international standard for building codes, according to Eric James, an architect with San Francisco-based Gensler’s New-port Beach office.
“They’re becoming more restrictive,” he said. “They’re site specific.”
Those norms could be more difficult for other countries to accept as the U.S. already has made strides in seismic safety.
Destruction from earthquakes has been more serious in foreign countries where buildings lack the reinforced steel that most U.S. buildings have, according to James.
Simple brick structures that aren’t reinforced with steel can be some of the most vulnerable, he added.
James has helped design a number of office buildings in the county, including branches for Charlotte, N.C.-based Bank of America Corp.
James and his colleagues use 3D computer models to test how well their designs will handle different earthquakes.
The models are probability based, and take into consideration different ways the earth can move as well as distance from epicenter.
While there’s no easy way to know how durable a building may be, “we’re fairly well prepared to handle things here,” James said.
Another factor affecting buildings during quakes is the soil they’re built on.
Feng says that the looseness of soil could cause more damage from the earth’s movement.
She studies the vibrations of buildings during earthquakes by using sensors to identify weak spots.
Data from July’s earthquake told her that the soil in her building had become looser.
The finding wasn’t enough to alarm her, but the data adds to a greater understanding of how safe OC’s buildings are.
Earthquakes in San Francisco in 1989 and in Kobe, Japan in 1995, along with the Northridge earthquake, have had the biggest impacts on design, James said.
“We’re constantly learning from past quakes,” said Feng.
