Thirty years of earthquake retrofit in the city of Los Angeles: Trends, drivers, and implications for seismic resilience

This study examines three decades of seismic retrofit activity in the City of Los Angeles to assess how the implementation has varied across space, time, and socially vulnerable communities. Using more than 29,000 building permits and census-tract sociodemographic data, we analyze temporal and spatial patterns for five vulnerable building types, with detailed focus on cripple-wall and soft-story woodframe structures. Time-series decomposition shows distinct adoption pathways with cripple-wall retrofits increasing gradually over many years and remaining relatively stable through economic disruptions. In contrast, soft-story retrofits rose sharply following the 2015 mandatory ordinance. Spatial autocorrelation analyses reveal significant clustering for both building types, but retrofit hot spots often diverge from the distribution of candidate buildings, indicating that policy, economic factors, and neighborhood-level decisions influence retrofit uptake. A scenario-based M 7.1 Puente Hills earthquake assessment shows that existing retrofits reduce expected direct losses by 68.6% for cripple-wall buildings and 41.2% for soft-story structures. However, the absolute reduction in losses was actually higher for soft-story buildings. The results also show statistically significant positive associations between social vulnerability and retrofit rates and benefits for cripple-wall buildings. However, the association for soft-story retrofits is negative and statistically significant. In general, the results underscore the progress made in reducing seismic vulnerability in the city and the need for more risk-aligned mitigation strategies.