The Northridge earthquake that hit 25 years ago offered alarming evidence of how vulnerable many types of buildings are to collapse from major shaking.
It toppled hundreds of apartments, smashed brittle concrete structures and tore apart brick buildings.
Since then, some cities have taken significant steps to make those buildings safer by requiring costly retrofitting aimed at protecting those inside and preserving the housing supply.
But many others have ignored the seismic threat. And that has created an uneven landscape that in the coming years will leave some cities significantly better prepared to withstand a big quake than others.
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