The Costs of Not Retrofitting From a Combined Engineering, Socioeconomic and Demographic Perspective

Abstract eng:
It is of great research interest to explore paths which reduce the severity of a natural disaster, where the severity of a natural disaster may be quantified as the product of exposure and vulnerability. Thus disaster reduction can be accomplished through decreasing either, or both, the natural hazard exposure and/or the community’s vulnerabilities. Communities have both physical and social vulnerabilities, and these are often linked. This study presents an approach at reducing the physical vulnerabilities of two communities through their residential building stock by modeling the social vulnerabilities and demonstrating the link between the two. Household dislocation, critical injuries, fatalities, and posttraumatic stress disorder (PTSD) were used as the vulnerability metrics. Two community-level retrofit plans were explored: one which retrofitted all low-code buildings to code level, and a second which retrofitted all low-code buildings to a high-code level. The retrofit plans were exemplified on two real communities in Los Angeles County, California, USA at the zip code level: 90011 the poorest zip code and 90077 the wealthiest zip code. Census data was used for modeling the social and physical vulnerabilities, including computing morbidity modification factors determined by the product of five socioeconomic and demographic factors for age, ethnicity/race, family structure, gender, and socioeconomic status. The costs of not retrofitting were demonstrated by comparing the vulnerability metrics and associated financial costs of the vulnerability metrics when a community decides to or not to retrofit their residential building stock. The results of the analyses revealed that the cost of not retrofitting was 9 to 446 critical injuries, 14 to 740 fatalities, 143 to 7,157 persons diagnosed with PTSD, and 127 to 1136 households forced to dislocate. Additionally, the results revealed that the financial cost of not retrofitting was US$80 million to US$4.5 billion. These numbers were computed for the poorest zip code for a maximum considered earthquake (MCE) scenario. The ranges are based on the retrofit level (either to code or to high code). This study quantified a social disaster index (SDI) as the product of exposure and the vulnerabilities. The analyses demonstrated a reduction in the SDI to occur when the physical vulnerabilities were reduced through retrofit. The reduction in SDI also demonstrated the influence of the social vulnerabilities by its great differences in value between the two study communities. There are other options for reducing the severity of natural disasters, including hazard exposure reduction, such as creating programs which offer incentives to households to relocate away from very hazardous regions (fault lines, coasts, floodplains, etc.). Addressing both the hazard exposure and vulnerabilities is likely the best solution for reducing the severity of future natural disasters.

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