Building on Fault Lines: Seismic Resilience and the Impact of 20th-Century Earthquakes and Housing Policy on 21st-Century Housing Affordability in San Francisco and Tokyo

Given the unpredictability of earthquakes, urban planning in seismically active regions must incorporate both immediate disaster mitigation and long-term resilience to protect populations and infrastructure. This project examines how major seismic events in 20th-century San Francisco and Tokyo catalyzed significant transformations in each city's approach to urban planning and how the persistent threat of seismic destruction has continued to influence 21st-century planning policies, particularly in terms of affordability, resilience, and sustainability. To explore these topics, this thesis develops a comparative case study using qualitative and quantitative data such as historical documents, government data, modern building codes and interviews with housing experts. I argue the stark differences in 21st-century planning priorities, housing affordability, and urban development between San Francisco and Tokyo are rooted in their contrasting approaches to 20th-century post-earthquake recovery, regulatory structures, and public attitudes toward resilience. This thesis also situates earthquake preparedness within broader regulatory and cultural contexts, arguing that Tokyo's centralized governance and national planning laws have enabled swift post-disaster adaptation, fostering a dynamic urban landscape through flexible zoning and high-density construction. In contrast, San Francisco's decentralized approach, characterized by strict zoning laws, historic preservation priorities, and a protracted permitting process, has created bureaucratic barriers that constrain new development and exacerbate housing shortages. This study highlights how regulatory frameworks shape both resilience and long-term urban growth, and contributes to a broader understanding of how cities can balance disaster preparedness, affordability, and sustainable urbanism in an era of increasing seismic uncertainty.