LOS ANGELES -- A massive earthquake rippling down the lower half of the San Andreas fault could cripple Southern California's economy and deal a severe shock to millions of workers and hundreds of thousands of businesses, according to a report released Tuesday by the U.S. Bureau of Labor Statistics.
Modeling the effects of a 7.8-magnitude earthquake, the likes of which has not been felt in Southern California since the 1850s but which geologists say is overdue, the study divided the region into areas of vulnerability, highlighting zones expected to receive either "very strong" or "destructive" shaking.
The study showed that roughly 430,000 businesses and 4.5 million employees would be affected in the hardest-hit zones: large swaths of a seven-county region that generates $206.5 billion in annual wages.
Underscoring the urgency of the report, Bureau of Labor Statistics Regional Commissioner Richard Holden said that a 7.8-magnitude earthquake -- much larger than the 6.7 quake that rocked the Los Angeles-area city of Northridge in 1994 -- would "put our jobs and economy at risk."
He said the findings show the need for businesses to focus not only on updating buildings to meet seismic safety codes, but on planning for worst-case scenarios. What's the backup plan, for example, if supply chains have been cut, roads blocked and electricity and water systems disrupted?
Amar Mann, a bureau economist and co-author of the study, said that a core of key professions is likely to be hurt the worst.
Straddling this high-risk part of the San Andreas fault are portions of Los Angeles, Orange, San Bernardino, Riverside, Imperial, Ventura and Kern counties, where "three out of four health care workers have jobs in the areas where the damage is expected to be the worst," Mann said.
"We think of the kids who will be in schools if this happens during the workweek and that's one thing, but 71 percent of educators are going to be in those areas too," he said. "This region is one of the last hubs in the nation for manufacturing. ... The lost economic activity as a result of this could be tremendous."
The study also shows how such an earthquake could bog down the national economy. The seven hard-hit counties account for roughly 1 out of every 15 workers in the U.S., Mann said, pointing out that the nationwide toll on unemployment and lost productivity could be severe.
Moreover, because rail systems, ports and roads are likely to be damaged, shipments by truck and train from the ports of Los Angeles and Long Beach would be affected. Over 23 percent of the total value of U.S. goods passed through the two ports in 2009, the study said.
The study, which excluded San Diego County because a major earthquake along the San Andreas is not expected to cause heavy damage there, did not predict the economic losses the region would suffer, but a 2008 report by the U.S. Geological Survey put it at $213 billion.
"The overall health of our community after the event would depend on how well all of our businesses are able to respond," said Lucy Jones, a seismologist at the Geological Survey whose work mapping earthquake scenarios buttressed the report.
"If you are a business and you feel an obligation to your employees, the issue is not just will they die -- probably they will not -- but will you be able to provide a job to your employees? You probably want to fulfill that obligation, not just for them, but for you and the rest of the community."