Bricks fell like rain in downtown Napa during the earthquake one week ago today.

In the aftermath, newspaper photos and TV video showed a car crushed by debris from a crumbling wall. Across the street, a brick façade collapsed onto the sidewalk. A gaping hole exposed the top floor of the courthouse, the post office buckled.

Fortunately, no one was killed.

The South Napa quake was Northern California’s largest in a quarter-century. But with a magnitude of 6.0, it rated only as a moderate quake, packing much less destructive power than the Big One that Californians expect and dread.

Striking at 3:20 a.m., the Napa quake shook countless thousands from their slumber.

Having had a week to assess its impact, it’s clear that this quake should be a wake-up call of another sort, too.

The bricks and building blocks littering streets and sidewalks are evidence that, for all of California’s seismic safety refinements, thousands of older buildings still aren’t ready to withstand even a mid-size earthquake.

In 1986, the state mandated upgrades for about 25,000 brick buildings in seismically active areas that didn’t meet modern earthquake safety standards. Three decades later, as many as 7,800 of those unreinforced masonry buildings haven’t been retrofitted.

In a quake, each of them could collapse or produce a lethal shower of bricks.

“This is not a question of ‘maybe these buildings will come down,’ ” U.S. Geological Survey seismologist Lucy Jones told the Los Angeles Times. “They absolutely will come down.”

That’s what happened in Paso Robles in 2003. Part of an unreinforced downtown building collapsed in a 6.5 magnitude quake, killing two people. Since then, almost 90 percent of the unreinforced buildings in San Luis Obispo have been retrofitted or demolished.

In Napa, some retrofitted buildings were damaged in last Sunday’s quake, but none came down.

About 200 of the remaining unreinforced buildings are here in Sonoma County, mainly in unincorporated areas such as Geyserville, Penngrove and communities along the Russian River, according to local building officials. They include retail shops, offices, restaurants, wineries and community halls.

Most of the high-risk buildings in Santa Rosa, Sonoma, Healdsburg and Petaluma have been strengthened. Santa Rosa mandated retrofits after dual earthquakes shook the city in 1969.

The state hasn’t updated its numbers since 2006, but Seismic Safety Commission officials don’t think many more buildings have been retrofitted since then.

A typical retrofit involves the placement of steel rods to secure brick walls to a building’s roof and foundation. The work can be expensive, but in 2010 voters approved an incentive for property owners to get the job down: exempting seismic retrofit projects from property tax reassessments.

In many communities, however, local officials have given in to complaints that retrofits are costly and waived deadlines for bringing buildings up to code. That’s dangerously short sighted.

Let the South Napa quake stand as a warning. A major quake is in California’s future. The only unknowns are when it will strike and where.

Scientists are developing an advance-warning system. It’s a promising system that could help first responders and even save lives. But it won’t keep roads from buckling and buildings from shaking. California residents need to prepare. That means having food, water, medicine and flashlights available. And it means bringing our homes and other buildings up to code before the earth starts shaking.