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Earthquakes: LA on track to have list of vulnerable 'soft-story' buildings by January

A construction worker using a chain on January 24, 1994, starts to cut up some of the destroyed walls in the courtyard of Northridge Meadow, the apartment complex that collapsed during the Northridge earthquake. Sixteen people were killed when the building collapsed during the quake. Councilman Tom LaBonge is now proposing an inventory of so-called
A construction worker using a chain on January 24, 1994, starts to cut up some of the destroyed walls in the courtyard of Northridge Meadow, the apartment complex that collapsed during the Northridge earthquake. Sixteen people were killed when the building collapsed during the quake. Councilman Tom LaBonge is now proposing an inventory of so-called "soft-story" buildings — those where the top stories could collapse onto the lower floor during a major temblor.
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The Los Angeles Department of Building and Safety is close to completing an inspection of 30,000 buildings to determine which are "soft-story" structures vulnerable to collapse in a strong earthquake, the head of the department said Wednesday.

Soft-story structures are typically multi-level buildings with open parking or commercial space on the first floor and usually supported by thin columns.

So far, city officials have identified about 2,000 such buildings in the San Fernando city council district represented by Paul Krekorian.

"Council District Two has the highest number of soft-story buildings," said Raymond Chan, head of the Department of Building and Safety. Chan spoke, along with seismologist Lucy Jones, as part of an update on efforts to make Los Angeles better prepared for a major earthquake.

Soft-story buildings are found throughout Los Angeles. During the 1994 Northridge earthquake, the soft-story Northridge Meadows apartment complex collapsed, killing 16 people.

Chan also said his team is working on an ordinance that will help find affordable ways to retrofit these structures.

"We hope that we can finish this program and get all buildings retrofitted in the time span of about 4 to 5 years," he said.

Earlier this year the City Council approved a motion to set aside roughly $382,000 to hire one structural engineer and two building inspectors for the project.

Chan said his department identified the 30,000 buildings to inspect using Google maps. Each inspector has been doing about 50 site visits a day to confirm which buildings are soft-story structures.

Lucy Jones, who is currently serving as Mayor Eric Garcetti's science advisor for seismic safety, added that non-ductile concrete buildings are also seismically vulnerable during a major quake.

However, she noted that it will be much harder to identify which concrete buildings are at risk since deficient non-ductile concrete structures cannot be identified by a site visit alone.

"It's going to require structural engineering analysis," she said.

In January of this year, researchers with the University of California gave L.A. city officials a list of about 1,500 potentially vulnerable concrete buildings.

Jones is in the process of preparing a report for Garcetti about the dangers posed by a major quake a long the San Andreas fault.

Such an event could also take out much of the city's communication infrastructure and cause serious damage to its waterways.

Jones said that about 85% of L.A.'s water comes from four aqueducts that each cross the San Andreas fault.

"The fault is going to move 10 to 30 feet and it will rip apart the aqueducts," Jones said.

The waterways in questions are the Colorado Aqueduct, the East and West Branches of the California Aqueduct and the Los Angeles Aqueduct.

Of the four, only the Los Angeles Aqueduct is under city control. Jones said it is also the easiest to retrofit since it only crosses the fault once. The Colorado Aqueduct crosses the San Andreas in 10 places, making it trickier to retrofit.

Jones said she's on target to have the report finished by the end of the year.

"I go on vacation January 1st," she laughed. "I've already got it planned and it's out of the country."