When a magnitude-6.4 earthquake rocked southern Taiwan on Saturday, images of building collapses quickly surfaced on social media and in local media reports. The damage, structural engineers said, was a sober reminder that these collapses would also probably occur in California should a massive temblor strike.
"What you're seeing in Taiwan in this recent earthquake is a microcosm of what could happen in a large earthquake occurring in a city like Los Angeles, where there are thousands more older susceptible buildings,” said Saif M. Hussain, who heads Seismic Structures International, a California-based structural engineering firm that specializes in earthquake resilience and safety.
Hussain, examining an online image of a 8- or 9-story building that had pancaked onto the first floor, said the collapse appeared to be a textbook case of an older concrete building that had a weak ground floor and was too brittle – or “non-ductile.” Sadly, he said, this is one of the most common seismic flaws in older, taller buildings around the world.
Taiwan generally has been following the same international building standards as California, Hussain said. In Los Angeles, non-ductile concrete buildings have collapsed in the 1971 Sylmar and 1994 Northridge earthquakes.
Today, in Los Angeles alone, more than 1,000 concrete structures built before 1980 — including landmark buildings in downtown, Hollywood and Westwood — require close scrutiny for seismic strengthening, according to a 2013 Times investigation.
A recent city law, spearheaded by Los Angeles Mayor Eric Garcetti, ordered property owners to retrofit older concrete buildings as well as wood-frame apartment complexes with weak first floors. The action will save lives, Garcetti said, when he signed the ordinance into law in October.
The law capped decades of efforts to strengthen these buildings. Past efforts to require retrofitting — or simply identify the most vulnerable buildings — died at City Hall over the question of cost. Landlords have long been concerned with the financial burden of retrofitting, which could cost as much as $130,000 for a wooden apartment and millions for a larger concrete building.
But some have questioned whether the law's deadlines should be accelerated, given the unpredictable nature of massive earthquakes. Under current law, property owners have seven years, upon notification, to fix wood apartments and 25 years to fix concrete buildings.
To begin the notification process, building officials have been working on finalizing a list of roughly 13,500 soft-story wooden buildings that might need closer structural evaluation. It will take longer for city officials to identify which concrete buildings will be included in the new retrofit regulations, officials said.
Hussain said he hopes the Taiwan earthquake might spur owners and officials to consider accelerating the retrofit deadlines. And other major cities in California have yet to pass retrofit laws on concrete buildings, which engineers say pose the greatest risk to loss of life in a major quake.
The Taiwan earthquake, which hit at 3:57 a.m. Saturday local time, or 11:57 a.m. Pacific time Friday, was particularly severe because it was very shallow — about 6 miles underground — and the epicenter was on the island, instead of offshore, said U.S. Geological Survey geophysicist Paul Caruso. People felt the earthquake as far away as mainland China.
Taiwan sits in a collision zone between the Philippine Sea and Eurasian plates, and, like California, is in a highly seismic area. Earthquake scientists and structural engineers in California will be sending reconnaissance teams in the coming days and weeks.
"The type of ground shaking in Taiwan is going to be very similar to what we have experienced, and what we will experience in the future,” Hussain said. “The source of the earthquake, the type of faulting, the depth of the earthquake — this is very similar to what we can expect in coastal California."