By SONALI KOHLI, JOE MOZINGO, LAURA J. NELSON and RONG-GONG LIN II

JUL 07, 2019 | 5:00 AM

The seismic one-two combo that hit Southern California last week left residents particularly unnerved because it robbed them of the single bit of solace that normally comes with a big quake: the sense that the worst is over.

After the 6.4 magnitude quake hit near Ridgecrest on Thursday, many expected aftershocks that would gradually decrease in strength and frequency. They’d been through it before, in Northridge, Sylmar and Whittier. But when a much larger 7.1 magnitude temblor struck Friday night, the shock quickly gave way to a newfound dread: What’s next?

Caltech seismologist Lucy Jones announced an 8% to 9% chance of an even bigger rupture coming within hours and days. Psyches spun out from Las Vegas to Long Beach, even as the risk was reduced to 3% by Saturday afternoon. The good news: Many decided it was finally time to get prepared.

“It’s only a matter of time,” said Kim Caldwell, 55, who has lived in Southern California all her life and experienced numerous quakes. She said she and her husband has been lax about keeping their earthquake supplies stocked and up to date at their home in Santa Ana. But if the first temblor didn’t jolt her into action, the second one certainly did.

“I’ve grown up with these,” she said. “This is the first one that was a sizable earthquake where the second one was actually bigger. Normally they trail off.”

Perhaps after a long earthquake drought residents needed the double warning.

Seismologists are constantly fighting against earthquake amnesia, trying to get people — many who have never experienced a major quake, with the last devastating one occurring a quarter-century ago in Northridge — to grasp the severity and ultimate inevitability of the threat and get prepared.

Friday’s quake was the largest in Southern California since 1999. Although it hit the Ridgecrest area of the high desert hard, it didn’t cause any notable damage in the Los Angeles area.

So while the seismic movements over the last few days were unsettling, only time will tell whether it will be enough of a push.

It’s one of the paradoxes of living in earthquake country that so many remain in denial despite the repeated warnings of the tectonic forces eternally poised to level the region.

Quake preparations can range from simple things — such as having earthquake kits and emergency plans ready — to more expensive items such as backup generators and quake insurance, and retrofitting buildings to better withstand shaking.

Less than 12% of California residents have insurance policies with quake coverage, according to state Department of Finance records.

Los Angeles, San Francisco and some other cities around California have required property owners to reinforce certain types of apartments that are vulnerable to collapse in a quake. L.A. has also required strengthening of brittle concrete buildings.

But experts say many seismic safety gaps remain, from bolting homes to foundations to dealing with chimneys that can collapse during heavy shaking.

If nothing else, the shaking of the last few days has many thinking about these issues.

“[I was] kind of a little shocked that there were two relatively large ones so close together and definitely started thinking about getting an emergency kit together,” said Ivan Castro, of Koreatown.

He was at a Dodgers game Friday, sitting in the top deck two rows from the rim of the stadium, when the earthquake hit. The crowd felt the rolling and then a jolt. “It’s pretty scary, if I’m being honest,” Castro said.

As a structural engineer, Castro, 31, is accustomed to reassuring his friends that they’ll probably be safe during an earthquake. He knows many structures are built or retrofitted to withstand such movement. But for the next week or so, he’ll be avoiding the potential death traps — unreinforced brick buildings.

“I’m even kind of hesitant to take elevators now,” he said.

Seismologists say the fault that ruptured would probably not set off the mighty, slumbering San Andreas, which is overdue for “the Big One” that every Californian should fear.

“It’s going to happen eventually,” Castro said. “I just got to tell myself be prepared as possible, talk to your friends, to your family; if you’re not at home, where are you going to meet?”

Jones said since officials began measuring earthquakes since 1932, there have been 22 of a magnitude 6 and above. Only two of those — including the one on July 4 — have been a foreshock to a larger one.

The last was in 1987, when a 6.2 magnitude quake struck south of the Salton Sea, followed by a 6.6 magnitude 12 hours later.

“It was really similar, it’s just that it was 30 years ago and nobody remembers,” said Jones, who has led the battle against earthquake amnesia.

She said roughly one in 20 earthquakes are followed by a bigger one within 30 days.

After Thursday’s quake, Paola Fernandez, 27, went online to research supply kits and disaster planning, and carried a battery pack to keep her phone charged.

But she didn’t think too much more about it, until the even the bigger one struck as she was at a downtown L.A. bar at happy hour. The potential severity of a closer seismic rupture hit home.

“This morning I was like, I need to start making a plan. I need to figure out what I need to do,” she said Saturday. “I need to prepare for any possibility of not being home or being stuck somewhere … all these worst-case scenarios come to mind.”

“I went to brunch and I was thinking to myself, ‘if this building started shaking where would I go?’” Fernandez said. How would she get to safety or connect with her family?

She identified an uncle in Colorado and made sure every family member had his number — in case of a massive earthquake or emergency they would each contact him to let him know they are safe.

Fernandez lives with her sister and father in Mt. Washington, down the street from her grandparents.

“For me I’m really concerned about my grandparents and like the older generation what could happen to them. I think that’s just one of my biggest concerns.” Her plan Saturday was to scour the city’s ShakeAlertLA app, and resources such as the Red Cross and government websites for preparation tips on what to put in her car and in her home’s earthquake kit.

She’d also go to her grandparents’ house and make sure their items were secured and not at risk of falling and hurting them.

“I feel like definitely it’s kind of like a wake-up call, it’s the reminder that we live in California and this is something that happens and we’ve been kind of waiting for it for decades now — the next Big One. It just feels like the likelihood of it happening is bigger than it was before the Fourth of July.”

“This is the geology of the land you live on so you just got to be careful.”

Times staff writers Deborah Netburn, Alex Wigglesworth and Karen Kaplan contributed to this report.