7 things you need to know about buildings that could kill in a major earthquake

The Northwest is threatened by earthquakes far more destructive than anything Washington state has experienced in modern times, a danger lawmakers have largely disregarded. In the first part of a continuing series, The Seattle Times examined officials’ neglect of the most vulnerable kind of building: old, brick structures called unreinforced masonry.

Here are answers to some common questions about unreinforced-masonry buildings.

How do I know if my building is unreinforced masonry?

If you live in Seattle, search our map of unreinforced-masonry buildings identified by the city.

It’s not always possible to tell just by looking. Sometimes brick walls have been plastered over, and sometimes what appears to be solid brick is actually veneer. There’s a good chance a building is unreinforced if it was built during the 1940s or earlier. Another telltale sign: bricks that look shorter than others, about every sixth row, that are actually turned on end.

Some California cities require warning signs on unretrofitted, unreinforced-masonry buildings, but there’s no such requirement in the Northwest.

How can I tell if an old brick building has been retrofitted?

Seattle’s list of unreinforced-masonry buildings includes some information on past retrofits, and identifies structures with no evidence of upgrades.

The most extensive retrofits are usually easy to spot. You can see sturdy cross beams inside or outside the building, and steel plates and columns shoring up old pillars and walls.

Rows of decorative rosettes on the building exterior indicate at least a basic type of retrofit, where walls and floors have been tied together via metal rods.

Does retrofitting make old brick buildings earthquake-proof?

No.

Even modern construction codes aren’t intended to prevent all earthquake damage. Their goal is to ensure that buildings won’t kill people when the ground shakes.

Well-retrofitted brick buildings shouldn’t collapse in an earthquake, but they could suffer serious damage.

Less extensive retrofits offer less protection — and in some cases may not be enough to prevent deaths.

What should I do if I’m in an unreinforced masonry building when an earthquake hits?

Your first instinct might be to run for the exits, but experts say that’s a very bad idea.

Drop to your knees, cover your head and neck, and if possible, crawl under a desk or table and hold on. If there’s nothing to get under, crouch next to an interior wall or piece of furniture, like a couch.

Don’t stand in a doorway.

If the urge to flee is overwhelming, consider this: One of the most dangerous places to be in an earthquake is near the exterior walls of any building, due to falling glass and chunks of facade. And no type of building is more likely to slough off deadly projectiles than one made of unreinforced brick or stone.

Even if the building collapses, you can survive if you’ve taken cover inside. Search-and-rescue teams are trained in collapse patterns and know how to locate voids and survivors.

A century-old building has survived multiple quakes. Why worry now?

None of Washington’s quakes over the past century have come close to the region’s worst-case seismic scenarios. In a coastal megaquake, the shaking can last as long as five minutes, compared to about 40 seconds during the 2001 Nisqually quake.

A quake on a shallow fault — such as the Seattle Fault, the Tacoma Fault or the Southern Whidbey Island Fault — will shake much harder than any modern quakes in the Puget Sound area.

And as buildings age, they deteriorate, which increases the risk of damage in subsequent earthquakes.

“People who say, ‘This building has been here for a hundred years, and nothing has happened’ don’t understand the risk from these more powerful quakes,” said Manish Chalana, who teaches urban design and planning at the University of Washington. “There’s some denial there.”

Will all unretrofitted brick buildings be toast in a major earthquake?

Not necessarily. Some unreinforced-masonry buildings are better constructed than others. And shaking can vary greatly based on soil conditions. Hard-packed glacial till, common on Seattle’s hills, doesn’t vibrate as much as looser soils, like those along river valleys and neighborhoods built on fill, including Sodo and parts of Pioneer Square.

Loose soils can also liquefy in a quake, undermining building foundations.

Here are maps of liquefaction hazard zones for Seattle, King County, Pierce County and other parts of the state.

What are the chances a Big One will strike during my lifetime?

The U.S. Geological Survey estimates a 10-14 percent chance of a magnitude 9 Cascadia megaquake over the next 50 years. Other scientists put the odds higher than 1 in 3 for a Cascadia megaquake of magnitude 8 or greater.

Unfortunately, The Big One isn’t necessarily the baddest one for individual cities. Seattle, Tacoma, Everett, Olympia and Bellingham all sit above or near shallow faults that can cause the ground to shake even more fiercely than in a coastal megaquake.

The Seattle fault last ruptured about 1,100 years ago. The USGS says there’s a 5 percent chance of another powerful quake under the Northwest’s biggest city within 50 years. The collective odds that one of the Puget Sound region’s many shallow faults will pop off in that same time period are three times higher.

But all the numbers simply represent scientists’ best understanding. The Earth is full of surprises. The quake that devastated the city of Christchurch, New Zealand in 2011 struck on a previously unknown fault.