Portland buildings vulnerable to collapse in an earthquake will soon come with a warning.

The City Council on Wednesday approved a policy that would require owners of brick and similar buildings to prominently post signs with the disclosure: "This is an unreinforced masonry building. Unreinforced masonry buildings may be unsafe in the event of a major earthquake."

The same warning would be distributed to tenants of the buildings.

The city is believed to have more than 1,600 unreinforced masonry buildings that have stood, on average, almost 90 years. The brittle materials holding those buildings up are less likely to survive a major earthquake such as the Cascadia subduction zone quake that experts say will likely hit the West Coast in the coming decades.

The warnings are intended as an interim measure. The city has signaled it won't require building owners to make fixes to prevent collapse for at least 20 years, and the city councilors who approved the warnings said they would allow residents and customers to weigh the risk for themselves.

But some owners of unreinforced masonry buildings opposed the placards, saying they exaggerate the risk and would scare away customers, making it harder to afford retrofits in the long run.

The signs will go up first in publicly owned buildings, mostly by Jan. 1. Most other buildings will be required to post the signs by March 1, but churches and nonprofit organizations would have two years to comply.

The ordinance was approved in a 3-0 vote. Commissioners Nick Fish and Chloe Eudaly were absent.

-- Elliot Njus