FAULT POSES DIRE QUAKE THREAT TO SAN DIEGO, REPORT SAYS
A magnitude 6.9 could sever utility services, damage 100K residences
A magnitude 6.9 earthquake on San Diego’s Rose Canyon Fault could damage 100,000 residences, cause widespread road and bridge failures, and make parts of Mission Bay sink about a foot, according to the most detailed disaster scenario ever done on the region.
Such a temblor also could cut gas and water service from La Jolla to the Silver Strand, collapse some of the city’s older municipal buildings, and close the San Diego-coronado Bridge, said a report by the San Diego chapter of the Earthquake Engineering Research Institute.
Parts of the fault would rupture the Earth’s surface and shift the landscape 6 to 7 feet, damaging streets so badly it would make
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it hard for police, firefighters and paramedics to get around.
The study, which was released Wednesday during the group’s quadrennial meeting in San Diego, estimates that the quake would inflict $38 billion in building and infrastructure damage, displacing 36,000 households and wreaking havoc on San Diego’s $245 billion economy.
“We’ve been working on this study for five years and it’s been a real wake-up call for stakeholders,” said Jorge Meneses, president of EERI-SAN Diego. “They were not aware of all of the possible consequences.
“But they have time to make San Diego more resilient to the kind of damages that could occur.”
EERI is a national technological society whose scientists and engineers evaluate the risk and consequence of large quakes in places like the Bay Area and Seattle’s Puget Sound. The group collaborates with government and first-responders to mitigate potential disaster.
In 2015, EERI focused its attention on the Rose Canyon Fault, which begins beneath the seafloor off Oceanside and extends south, coming ashore in La
Jolla, where it proceeds through Mount Soledad and Rose Canyon, along Interstate 5.
Scientists say the fault then cuts through Old Town, Little Italy and downtown San Diego before heading offshore at the Silver Strand and stretching down the coast to roughly Tijuana. Branches of the fault exist beneath San Diego International Airport, which handles nearly 70,000 airline passengers a day, as well as the San Diego Convention Center and Tenth Avenue Marine Terminal.
The fault — like the better-known San Andreas — is a strike-slip system. When it slips, one side of the fault moves horizontally in relation to the other.
Meneses and other scientists don’t believe that a quake is imminent on the Rose Canyon Fault, which appears to produce a major temblor roughly once every 700 years. The last significant quake, measuring 6.0, occurred in 1862. The new report says there’s only an 18 percent chance that a fault within the county, or just offshore, would produce a 6.7 or larger quake in the next 30 years.
But the Rose Canyon Fault isn’t well understood, or even well-known. Meneses
joked during Wednesday’s conference that when he mentions Rose Canyon some people ask, “Is that a new restaurant?”
Scientists want to make sure that San Diego doesn’t get caught off guard the way Los Angeles did in 1994 when the 6.7 Northridge quake erupted on an unknown fault. Nearly 60 people were killed.
EERI produced a preliminary report in 2017 that said a 6.9 quake could cause $40 billion in property damage and kill 1,000 to 2,000 people. Researchers said a lot of the fatalities could result from an offshore landslide that would produce a tsunami that would hit the Silver Strand.
The final report downplays the prospect of a tsunami and trims the estimated economic damage. But the study says that a quake lasting 15 to 30 seconds could cause extraordinary shaking — enough to trigger landslides on Point Loma and Mount Soledad.
A lot of the most intense energy would hit coastal communities from San Diego down through Tijuana, areas that are densely populated and highly dependent on imported gas and water.
The quake would cause moderate to severe damage to roughly 120,000 of the nearly 700,000 structures that exist countywide, with especially heavy damage to schools, health care and government facilities in coastal areas, where shaking would cause liquefaction, the report adds.
Liquefaction means that loose, saturated soil essentially liquefies during shaking, potentially causing buildings to tilt, sink or fall apart. It can also snap utility lines.
Researchers estimate that half of the schools and hospitals in the county would be able to function on only a limited basis, and that many people would have to flee the coast.
The report further says that, “Department of Defense facilities, particularly those encircling San Diego Bay, will be exposed to severe ground shaking and liquefaction and will likely face widespread damage to older buildings, waterfront structures, and lifeline utility infrastructure.”
Before the end of this year, those facilities will be responsible for serving three nuclear-powered Navy aircraft carriers.
The Tenth Avenue Marine Terminal and San Diego International Airport also could suffer a loss of gas and petroleum lines, which could affect commercial airline traffic as well as passenger ships. The airport serves nearly 25 million passengers a year.
The San Diego-coronado Bridge has undergone seismic retrofitting and would likely survive the earthquake. But researchers said that feeder streets could be so heavily damaged that the bridge would be knocked out of service.
The report also says that the Coronado Fire Department could lose access to water, crippling its ability to fight fire.
The predictions elicited some sobering reactions on Wednesday.
“I live in the coastal zone and was not aware that I could be out of water for three or four months,” said Ali Fattah, a senior research engineer for the city of San Diego.
Gary Johnston saw an upside: “The probability of a quake like this is low, but the consequences are high,” said Johnston, chief resilience officer for the county Office of Emergency Services. “It focuses us on things we can do now to mitigate and prepare for an earthquake.”