The Los Angeles City Council on Friday passed an ordinance that will require landlords of thousands of apartment buildings to retrofit their buildings to better withstand earthquakes. Mayor Eric Garcetti signed the ordinance immediately afterward.

The ordinance, touted as the nation’s most sweeping earthquake safety rule, will require the owners of an estimated 15,000 “soft story” structures – mostly apartment buildings – to spend tens of thousands of dollars each to install steel bracing or other materials to reinforce beams so that they don’t buckle during a major quake. During the 1994 Northridge earthquake, an apartment building in Northridge collapsed, killing 16 people.

Retrofit costs can range from $20,000 for small apartment buildings to several hundred thousand dollars for multistory concrete buildings.

“Today, Los Angeles makes good on our promise to take action before it’s too late,” Garcetti said as he signed the ordinance. “We’re leading the nation in requiring this level of building safety retrofit before, not after, the big quake that we know is coming.”

But the Council left for another day the thorny issue of just how those costs would be distributed. One plan would allow apartment building landlords to pass through the state-mandated maximum of $75 a month to renters; another plan would only pass through half of that amount – $38 a month – to renters, leaving the landlord to shoulder the rest.

San Francisco this week voted to allow landlords to pass along up to $75 a month to tenants to cover the costs. But the Apartment Association of Greater Los Angeles, representing local landlords, has argued in favor of the cost sharing approach, saying that state funds should be used to reduce the landlords’ share.