After major temblors on July 4 and 5, structural engineers descended on Ridgecrest expecting to study destruction from the largest earthquake to hit Southern California in nearly 20 years.

They found relatively little.

Yes, mobile homes were torn off foundations, chimneys fell, gas lines leaked and some homes caught fire. But overall, most buildings did fine — and many businesses were up and running within a day or two of the biggest shock, a magnitude 7.1.

“Ridgecrest, I’m just amazed,” California Earthquake Authority structural engineer Janiele Maffei said of the light damage.


But the outcome in Ridgecrest shouldn’t provide solace to California’s biggest cities.

The Mojave Desert town remained largely unscathed because its building stock was relatively new and remarkably resilient. Many homes are one or two stories, built in the 1980s. It lacks the kind of structures that experts say are most vulnerable in a big quake — unreinforced masonry, brittle concrete, so-called soft story apartments and single-family homes not bolted to their foundations.

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As a result, Ridgecrest suffered far less damage than cities hit by less powerful quakes in recent years, including Napa and Paso Robles, where older buildings in the downtown areas crumbled amid the shaking.


Experts were quick to point out that last week’s quakes would have proved far more devastating had they been located near bigger cities filled with more susceptible buildings.

(Los Angeles Times)

“You take a 7.1 and put it into the Hollywood fault or Newport-Inglewood fault in Long Beach — we’re going to see substantially different levels of damage,” said Ken O’Dell, president of the Structural Engineers Assn. of Southern California. “Ridgecrest did a very good job surviving this particular 7.1.”

Keith Porter, a nationally renowned earthquake engineer and research professor at the University of Colorado Boulder, said Ridgecrest’s result should not be seen as a “victory lap.”


“We still have dangerous buildings, and we still have a building code that is not optimal and doesn’t protect society as well as it could,” he said. “Instead of a dozen collapsed manufactured homes, hundreds or thousands of collapsed manufactured homes. Instead of four or so building fires, hundreds of building fires.”

Progress has been made by cities — Los Angeles and San Francisco among them — to require some building retrofits. But even those large population centers have not mandated retrofits of all the types of structures engineers worry about. And authorities in many suburban areas — including in Silicon Valley, San Mateo County and the beach cities of L.A. County’s South Bay — haven’t ordered flimsy apartment buildings to be strengthened.

Many cities in Riverside and San Bernardino counties haven’t required fixes to brick buildings, a vulnerability Californians have known about for a century.

A U.S. Geological Survey simulation said a plausible magnitude 7.1 earthquake on the Hayward fault in the Bay Area could kill 800 people, burn the equivalent of 52,000 single-family homes and displace 400,000 people, worsening the region’s housing crisis.


And a hypothetical magnitude 7.8 earthquake that would send violent shaking waves along a 186-mile section of the southern San Andreas fault could kill 1,800 people, leave 50,000 injured and cause lasting harm to Southern California’s economy.

Such a direct hit “would take days or weeks to get to the place we are [at in Ridgecrest] — gearing up toward restoration and early recovery,” said Laurie Johnson, president of the Earthquake Engineering Research Institute.

1 / 42 Dan Tolbert, 62, spends time with his dogs as he and his wife, Ronnie, 60, prepare to bed down for the night on a pair of mattresses in front of their earthquake-damaged home in Trona on July 10. Their night was interrupted when a scorpion crawled on their mattresses and they ended up spending the night in their truck. “If we keep feeling tremors tomorrow we’ll be out here again,” Ronnie said. (Genaro Molina / Los Angeles Times) 2 / 42 Karen Byrd, 39, collects photo frames knocked off the wall at her home in Trona, Calif. (Irfan Khan / Los Angeles Times) 3 / 42 Ronnie Tolbert, left, delivers food to Robert VanHorn, 81, almost a week after a 7.1 earthquake near Trona. (Genaro Molina / Los Angeles Times) 4 / 42 Benny Eldridge, 76, looks at a quake-damaged room in his Trona home, which he helped build with his father-in-law in 1961. The house has been red-tagged. (Genaro Molina / Los Angeles Times) 5 / 42 Benny Eldridge, 76, and his wife, Anna Sue, 75, sit in front of their damaged home in Trona. (Genaro Molina / Los Angeles Times) 6 / 42 Joyce Harrison Moore, 72, looks out from her damaged home almost a week after a pair of earthquakes battered Trona. “This town will either die or get back on its feet,” Moore said. (Genaro Molina / Los Angeles Times) 7 / 42 Ronnie Tolbert stands beside her damaged fireplace. (Genaro Molina / Los Angeles Times) 8 / 42 Valerie Helton, 60, facing the camera, receives a hug of support from Ronnie Tolbert. Helton and her daughter Jessica Sizemore Helton, left, have refused to leave their home since last week’s quakes. “This is all I have,” said Sizemore Helton. (Genaro Molina / Los Angeles Times) 9 / 42 Ralph “Zeb” Haleman, 67, carries cases of water home Sunday in Trona, Calif., where residents were still without water and electricity was spotty after last week’s quakes. (Irfan Khan / Los Angeles Times) 10 / 42 Kay Byrd, 64, gives herself an insulin shot. Byrd and her family are camping outside in Trona, Calif., wary of returning home after major earthquakes. (Irfan Khan / Los Angeles Times) 11 / 42 Brooke Thompson, 8, plays on the sleeping bag that her family slept in after a pair of major earthquakes drove them out of their home in Trona, Calif. (Irfan Khan / Los Angeles Times) 12 / 42 The Byrd family has breakfast next to where they spent the night under a salt cedar tree, afraid to return to their Trona, Calif., home of 21 years after major earthquakes. (Irfan Khan / Los Angeles Times) 13 / 42 Ronnie Tolbert, left, and her husband, Danny, sleep on mattresses in the front yard of their Trona home, which was damaged in a 7.1 magnitude earthquake. (Robert Gauthier / Los Angeles Times) 14 / 42 The Horta family sleeps in the back of their pickup truck in a fire station parking lot in Trona as the sun rises hours after being forced from their home by a magnitude 7.1 earthquake. (Robert Gauthier / Los Angeles Times) 15 / 42 Kathy Vander Housen, 76 hugs her friend Claire Barker, 76, after Barker told her that she had found her two cats. Vander Housen’s mobile home in Trona had been yellow-tagged by county inspectors, but she did not want to leave without the cats, which had been hiding since the earthquake (Irfan Khan / Los Angeles Times) 16 / 42 Buckled asphalt courses through a parking lot near Trona Rd. in Argus. (Robert Gauthier / Los Angeles Times) 17 / 42 Sammy Chute cuddles Gerard as her family in Trona prepares to evacuate to Ridgecrest, abandoning their home that was knocked off its foundation during a 7.1 earthquake. (Robert Gauthier / Los Angeles Times) 18 / 42 Charles Ware, 68, in his Trona front yard the morning after a 7.1 magnitude earthquake severely damaged his home. Ware said he invested all he had into this house two years ago, doesn’t have earthquake insurance and is afraid he may not be able to rebuild. He was on the phone with his brother in San Diego when the quake hit. “I got to ride it out with my brother,” he said. (Robert Gauthier / Los Angeles Times) 19 / 42 A customer rummages for a six-pack of beer at a damaged Shell food mart in Trona the day after a 7.1 earthquake. (Robert Gauthier / Los Angeles Times) 20 / 42 Hundreds of residents of Ridgecrest, Calif., and surrounding communities attend a town hall meeting at Kerr McGee Community Center about the response to recent major earthquakes. (Irfan Khan / Los Angeles Times) 21 / 42 Christian Fellowship of Trona congregants pray after holding a quick meeting on how to help other community members. (Irfan Khan / Los Angeles Times) 22 / 42 Kern County firemen tackle a fire on Saturday morning at Town and Country Mobile Home Park in Ridgcrest. (Irfan Khan / Los Angeles Times) 23 / 42 Jamie L. Acevedo sits outside her damaged Trona home, waiting to evacuate to Ridgecrest the morning after a 7.1 magnitude earthquake knocked her home off its foundation. (Robert Gauthier / Los Angeles Times) 24 / 42 Gas station owner Roger Sandoval faces the possibility of having to shut his Trona business after a 7.1 earthquake apparently damaged the supply tanks near the pumps. (Robert Gauthier / Los Angeles Times) 25 / 42 Chavela Padilla, left, an emergency response team volunteer, walks with Ronnie Tolbert amid quake-toppled items in Tobert’s Trona home. The damage occurred in a 7.1 temblor hours earlier. (Robert Gauthier / Los Angeles Times) 26 / 42 Chavela Padilla, a Trona emergency response team volunteer, enters her car after checking on a neighbor as her two young boys, Joey, 8, right, and Jimmy, 5, sleep in the back seat at close to 3 a.m. The boys were too scared to be home after experiencing a 7.1 earthquake hours earlier. (Robert Gauthier / Los Angeles Times) 27 / 42 Chavela Padilla, right, an emergency response team member walks with Ronnie Tolbert amid quake-toppled items in Tolbert’s Trona home. (Robert Gauthier / Los Angeles Times) 28 / 42 Brothers Joey, 8, right, and Jimmy Raya, 5, sleep in the back seat of their mother’s car in the parking lot of San Bernardino County Fire Station 57 in Trona after their home was damaged in a 7.1 magnitude earthquake hours earlier. (Robert Gauthier / Los Angeles Times) 29 / 42 Chavela Padilla, a Trona emergcency response team volunteer, assists her neighbor Alicia Marines, 72, who was injured while trying to escape her home during a 7.1 magnitude earthquake. Marines was evacuated to the local fire station. James Raya, Padilla’s husband and also a volunteer, looks on. (Robert Gauthier / Los Angeles Times) 30 / 42 Chavela Padilla, a Trona emergency response team volunteer, stands in the bloody footprints left by homeowner Alicia Marines, 72, who was injured during a 7.1 magnitude earthquake. Padilla volunteered to check on Marines’ residence and collect some fresh clothes. (Robert Gauthier / Los Angeles Times) 31 / 42 Ronnie Tolbert sorts through toppled belongings in her Trona home, damaged in a 7.1 magnitude earthquake hours earlier. (Robert Gauthier / Los Angeles Times) 32 / 42 The aftermath of Friday’s earthquake at a Ridgecrest liquor store. (Robyn Beck / AFP/Getty Images) 33 / 42 Work on Route 178 between Trona and Ridgecrest. (Etienne Laurent / EPA-EFE/REX ) 34 / 42 Workers fill large holes left in Highway 178 between Trona and Ridgecrest by Friday night’s 7.1 earthquake. (Etienne Laurent / EPA-EFE/REX ) 35 / 42 Highway workers repair roadway near Ridgecrest on Saturday morning. (Robyn Beck / AFP/Getty Images) 36 / 42 Police and emergency services respond to a fire at a building on Highway 178. (Etienne Laurent / EPA-EFE/REX ) 37 / 42 Firefighters respond to a fire at a building on Highway 178 after Friday night’s earthquake near Ridgecrest. (Etienne Laurent / EPA-EFE/REX ) 38 / 42 In Ridgecrest, Davia Speed and Peyton Speed, holding 1-month-old Lillian, get into their car after Friday night’s 7.1 earthquake. (Irfan Khan / Los Angeles Times) 39 / 42 Dawn Inscore leaves her apartment on Ridgecrest Boulevard with her child after the Friday night earthquake. (Irfan Khan / Los Angeles Times) 40 / 42 A fire burns behind Casa Corona restaurant in Ridgecrest after Friday’s earthquake. (Jessica Weston / The Daily Independent/Associated Press) 41 / 42 Carmen Rivera, 65, walks her dog Ash past a dislodged home in Torusdale Estates mobile home park in Ridgecrest. (Irfan Khan / Los Angeles Times) 42 / 42 Zoe Pineda, 7, helps clean up the library in Ridgecrest after the Fourth of July quake. (Irfan Khan / Los Angeles Times)

Why Ridgecrest was spared


There are a number of reasons why Ridgecrest was largely spared.

The town, which began growing up the near Naval Air Weapons Station China Lake during World War II, does not have a stock of unretrofitted brick buildings like those constructed before the 1933 Long Beach earthquake, said USGS seismologist Susan Hough. Unretrofitted brick buildings are a major killer in quakes, causing at least five deaths in San Francisco during the 1989 magnitude 6.9 Loma Prieta earthquake and two fatalities in the 2003 magnitude 6.5 Paso Robles earthquake.

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There are also very few “soft story” apartments with weak ground floors built to accommodate parking — likely, Hough said, a result of “having enough room to not ever need high-density housing.” A soft-story apartment collapse killed 16 people in the 6.7 Northridge earthquake in 1994.


And because they are newer, the single-family homes in Ridgecrest lacked the vulnerability of many Southern California and Bay Area pre-1980 wood-frame houses built with a handful of steps above the ground. Sharp shaking can snap the wood supports connecting such homes to their foundations. A retrofit to brace and bolt the structure can cost several thousands of dollars — but repairing the problem after a quake can cost hundreds of thousands of dollars.

Repeating the July 4 and 5 quakes in the Bay Area and Southern California would result “in a lot of homes off their foundations,” Maffei said. “Without retrofits, the Bay Area and Los Angeles do not have resilient housing.”

There are at least 1 million of these vulnerable homes in California, but Ridgecrest has very few.

Joaquin Vasquez, 12, looks over earthquake damaged shelves as his father, Alex Vasquez, cleans up their garage in Ridgecrest. “We lucked out. We didn’t get much damage,” Alex said. (Genaro Molina / Los Angeles Times)


The more obvious signs of damage in Ridgecrest did not make many structures uninhabitable — cracked concrete walls surrounding yards or a broken decorative brick façade on a home, said Southern California structural engineer Wayne Chang, who visited the region Sunday and shared his observations with the Earthquake Engineering Research Institute.

Some of the worst damage was to mobile homes, which often are not secured to their foundations, engineers said.

The happenstances of geology and geography also worked in the town’s favor.

The magnitude 7.1 earthquake started at an epicenter 10 miles northeast of central Ridgecrest. But it occurred on a fault that focused the worst shaking waves away from Ridgecrest and Trona, to the northwest and southeast, respectively, of the epicenter, and into sparsely populated areas, Caltech seismologist Egill Hauksson said.


On the Modified Mercalli Intensity Scale, Ridgecrest endured “very strong,” or level 7 shaking, enough to break chimneys and damage badly designed structures but keep damage negligible in well-designed buildings. Trona got a level 6 “strong” shaking.

By contrast, much of the San Fernando and Santa Clarita valleys saw at least level 8, or “severe,” shaking during the Northridge quake — an intensity that can greatly damage poorly built structures. (The shaking nearly caused a new steel frame Auto Club building in Santa Clarita to collapse and seriously damaged or destroyed 200 apartment buildings.)

Even though the Northridge earthquake produced much less total energy than the temblor on July 5, its location caused shaking to be worse directly underneath a highly populated area.

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Trona, an older city, was more heavily hit than Ridgecrest.

Although the shaking was less intense, Trona’s location on soft sediments that have eroded off a mountainside — known as an alluvial fan — caused the ground to act like quicksand, O’Dell said.

“That spreading of the soil undermined the foundations,” he said, causing the base of buildings to come apart.

Chang said Trona’s well-maintained homes seemed to withstand the shaking well, but some abandoned and unoccupied houses suffered collapsed walls.


There are few public details so far about the structural damage suffered at the Naval Air Weapons Station, which has been directly on top of recent earthquakes. Conditions have forced personnel to evacuate.

So far, authorities believe one person has died as a result of one of last week’s earthquakes — a Nevada man found pinned under his Jeep after the vehicle fell off its jacks.

What should be done

Engineers and safety advocates say more can be done before the next big quake hits California. That includes bolting bookshelves to walls, arming kitchen cabinets and clothing dressers with toddler-safe locks, and using quake putty to affix breakable items to shelves.


Porter wants lawmakers to look to strengthen the state’s minimum building requirements, which he says currently allow for construction just strong enough to not collapse in a quake.

“People think a new building is earthquake-proof. But really, all it’s supposed to do is not collapse and kill you,” Porter said. “The damage can be so costly that you can’t afford to fix it; that it doesn’t make sense to fix it.”

He urged lawmakers to reconsider a measure vetoed by then-Gov. Jerry Brown in 2018, which called for a tougher construction code to keep new buildings usable after a major earthquake.

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Porter also said cities need to tackle the vulnerabilities presented by some of California’s largest buildings.

Los Angeles, for instance, has yet to decide how it wants to address the risk of steel moment frame buildings constructed before the Northridge quake; the USGS has said it is plausible that five high-rise steel buildings in Southern California could topple in a magnitude 7.8 quake.

San Francisco has yet to decide on how it wants to deal with its stock of about 3,000 potentially vulnerable brittle concrete buildings, the kind that collapsed in the Northridge and Sylmar earthquakes.

“If we think it’s expensive to fix those buildings, wait until we get the bill for not fixing them,” Porter said. If a financial district is obliterated by the collapse of a single steel skyscraper, Porter said, “who is going to want to go into all the other ones that didn’t collapse? Our trust in those buildings will evaporate.”


It’s time to move beyond simply preparing an earthquake kit as the main way to prepare for the Big One, O’Dell said.

“Being prepared is more than having your kit stocked, it’s more than having a hard hat under your bed,” O’Dell said. “We need to be preparing our buildings.”

ron.lin@latimes.com

@ronlin