Owners of Portland's vintage stock of brick buildings have been worrying about a looming threat: an earthquake retrofit mandate that could cost them hundreds of thousands of dollars.

But earthquake experts point to another threat: the ever-increasing chance that a large earthquake will hit the Portland area, sending many of those buildings crumbling.

As the mandate goes before the Portland City Council on Wednesday, Mayor Ted Wheeler has proposed softening it for most buildings and extending the deadline to 20 years from the 10 to 15 proposed by an advisory committee, concessions that his staff said would ease the burden on "mom and pop" building owners.

Earthquake experts say putting any requirements on the books is a step in the right direction, but they also say it's a half-measure that will only delay the inevitable. And extending the deadline means a greater chance an earthquake catches those unreinforced masonry buildings unprepared. (Schools, critical buildings and large gathering places would still be held to higher standards.)

"This particular mandate is giving some options to owners, which is OK to start," said Franz Rad, a professor of civil and environmental engineering at Portland State University. "But what we really need to do down the line is retrofit all of them to at least a minimum level and/or eliminate the ones that are too expensive to retrofit.

"They are indeed death traps for the big earthquake we're expecting."

Wheeler's proposal would require owners of most unreinforced brick buildings to bolt the building's roof to its walls and reinforce the parapet, the short wall that extends around the roof of most brick buildings. That's intended to prevent the wall from peeling away during a quake, damage that can occur in even light shaking, posing danger to people inside and outside the building.

But Wheeler has proposed to remove a requirement that floors be bolted to walls. Unsecured floors can push against brittle brick walls in a quake, so bolting them can help prevent multistory buildings from collapsing — but the fix is far more invasive and expensive.

"That piece is where it gets very messy," said Kathy Rogers, who owns an unreinforced brick apartment building in Southeast Portland and is an organizer of Save Portland Buildings, a group that has opposed the mandate.

Rogers said most owners of unreinforced masonry buildings welcomed the 20-year timeline and that the requirement to fasten floors to walls has, at least for now, been taken off the table. Those upgrades would require the ouster of businesses and apartment residents while the work is underway, likely closing businesses and forcing residents to find a new place to live.

The remaining roof-retrofit requirements, while still a hefty financial lift, are easier to take on — and more worth the money, Rogers said.

"If you can brace the parapets and sturdy up the frame, you get 80 percent of the benefit for about 20 percent of the overall cost," she said.

Meanwhile, the city will seek statewide funding to help finance the retrofit work, and the city will also develop a property tax exemption to further offset the cost.

The city is also taking a page from California's book to shame building owners into completing the retrofits. That state requires owners of unreinforced masonry buildings to post signs warning that they "may be unsafe in the event of a major earthquake." The Portland City Council is considering asking its staff to write such an ordinance.

Portland has a stock of 1,600 unreinforced brick buildings in part because it's suffered few even minor earthquakes over the years, said Christopher Higgins, a structural engineering professor at Oregon State University. California cities, on the other hand, have had numerous smaller quakes that have winnowed those most susceptible to quakes.

Unreinforced brick buildings are just one type of construction at risk. San Francisco is trying to address the risk of so-called "soft-story" wood-framed buildings, built with relatively weak ground floors, and it also has a stock of brittle concrete buildings that could collapse in a quake.

Portland also likely has other building types to worry about, along with fragile bridges and utility lines.

"Our problem with unreinforced masonry is just the beginning," Higgins said. "We have very fragile infrastructure in this state for seismic."

Oregon sits about 70 miles from the Cascadia subduction zone, an offshore fault line that's overdue for a big quake. When it hits, Portland potentially faces $80 billion in building damage, tens of thousands of people wounded or killed, and more than 250,000 residents facing long-term displacement, according to a state report released earlier this year.

The odds of a quake with a magnitude of 8 or greater that affects Portland is about 22 to 26 percent in the next 50 years, said Chris Goldfinger, an Oregon State University professor of geology and geophysics and a leading expert in the Cascadia subduction zone.

But there are other faults near Portland about which little is known. They could increase the odds of a significant quake at any time.

That could mean an unexpected wake-up call for Portlanders before the "Big One" hits.

"In the future, especially if we get a 5.8 in or near Portland area before the Cascadia Quake, people will be more inclined to retrofit weaker structures," Rad said, adding: "The ones that still remain."

-- Elliot Njus

enjus@oregonian.com

503-294-5034

@enjus