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Anticipating when the ‘Big One’ strikes Los Angeles Basin

Fifty-two years ago this week, a 6.6 magnitude earthquake struck the Sylmar region of Los Angeles, resulting in widespread damage across the southland leaving 64 persons dead and more than […]

Earthquake after math

Fifty-two years ago this week, a 6.6 magnitude earthquake struck the Sylmar region of Los Angeles, resulting in widespread damage across the southland leaving 64 persons dead and more than 2,000 injured.

But what effect would a magnitude 7.8 earthquake–such as the one that struck Turkey on Monday–have on the Los Angeles Basin?

Experts say the damage would be so widespread and intense it may be hard to fathom.

Angelenos have long anticipated the fallout after the “Big One.” Scientists have spent years developing simulations of how that scenario would play out.

A quake as strong as magnitude 8.2 is possible on the southern San Andreas fault and would bring disaster to all of Southern California simultaneously, with the fault rupturing from near the Mexican border to Monterey County. The City of Palmdale sits directly on the San Andreas fault. Such an earthquake would cause widespread damage from Palm Springs to San Luis Obispo — and everything in between, experts say.

“The 7.8 magnitude earthquake in Turkey means the fault was at least 200 to 300 kilometers long,” said Dr. Lucy Jones, seismologist with the U.S. Geological Survey and commonly referred to locally as the “earthquake lady.” Jones explained that Turkey utilizes the same International Building Code as does Los Angeles — but they don’t have the same modern protections as found locally.

“That type of earthquake is not as ‘far away’ from us as we hope it would be,” she said. “You saw the destruction there because those buildings were not built to the standards necessary. The continued shaking caused the corners of the structures to collapse inward.”

Jones likened the destruction to the collapse of Olive View Hospital in Sylmar in 1971. In LA, pre-1980 buildings would collapse similarly if not properly retrofitted.

“All building codes were improved after the Sylmar quake,” Jones said, “and while Southland buildings likely wouldn’t collapse in such a strong earthquake, they would be a total loss and uninhabitable.”

In 2008, the U.S. Geological Survey and a host of other state government agencies and academics published a study called the ShakeOut Scenario that told the story of what could happen if a magnitude 7.8 earthquake returned to Southern California.

A magnitude 7.8 earthquake would be “so powerful that it causes widespread damage and consequently affects lives and livelihoods of all southern Californians. A catastrophe is a disaster that runs amok when a society is not prepared for the amount of disruption that occurs,” the report said.

Among the impacts, the report found:

•  The death toll could be among the worst for a natural disaster in U.S. history: nearly 1,800.

•  Los Angeles County could suffer the highest death toll, more than 1,000, followed by Orange County, with more than 350 dead.

•  Nearly 50,000 could be injured.

•  Main freeways to Las Vegas and Phoenix that cross the San Andreas fault would be destroyed.

•  Some 500,000 to 1 million people could be displaced from their homes.

•  Southern California could be isolated for some time, with the region surrounded by mountains and earthquake faults.

•  Major utilities such as gas, power and cell service would likely be severely compromised.

The last California seismic event that reached magnitude 7.8 was the great San Francisco earthquake of 1906. In Southern California, a magnitude 7.8 quake struck in 1857. (The magnitude 6.7 Northridge earthquake, which occurred on a much smaller fault in the San Fernando Valley, was 45 times weaker than the Ft. Tejon quake.)

The last two big earthquakes to strike Los Angeles — the 1971 Sylmar quake and 1994 Northridge quake — caused destruction and loss of life. But the worst damage was concentrated in relatively small areas and did not halt daily life across all of Southern California.

Experts have long warned that a significantly larger quake will eventually strike and that the toll will be far greater.

The San Andreas fault produced the epic 1906 quake that destroyed San Francisco. The Hayward fault in the East Bay also poses a major threat, experts say.

A landmark report by the U.S. Geological Survey in 2018 estimates that at least 800 people could be killed and 18,000 more injured in a magnitude 7 earthquake on the Hayward fault centered below Oakland.

The Hayward fault is most dangerous because it traverses through some of the most heavily populated parts of the Bay Area, spanning the length of the East Bay from the San Pablo Bay through Berkeley, Oakland, Hayward, Fremont and into Milpitas.

For all the devastation of the 1906 San Francisco earthquake, it was centered off the coast in the Pacific Ocean.

Building standards in California are significantly stronger. Images in Turkey and Syria show countless toppled buildings. California has been working to improve seismic safety rules for vulnerable buildings.

The ShakeOut scenario focused on unretrofitted brick buildings, brittle concrete buildings and so-called soft-story apartment buildings. Some cities including Los Angeles and San Francisco have been pushing retrofits for these types of structures.

Last year, L.A. announced a major milestone: More than 8,000 seismically vulnerable buildings have been retrofitted across the city at an estimated cost of $1.3 billion. The improvements mark the biggest advance in seismic upgrades in decades but still leave thousands of buildings vulnerable to damage or even collapse in a catastrophic temblor.