Substitute or complement? How social capital, age and socioeconomic status interacted to impact mortality in Japan's 3/11 tsunami.

Background: Research underscoring the critical nature of social capital and collective action during crises often overlooks the ways that social ties interact with vulnerability factors such as age and socioeconomic status.

Methods: We use three different data structures and five types of regression models to study mortality rates across 542 inundated neighborhoods from nearly 40 cities, towns, and villages in Japan's Tohoku region which was flooded by the 11 March 2011 tsunami.

Results: Controlling for factors thought important in past studies - including geographic administrative, and demographic conditions - we find that social capital interacts with age and socioeconomic status to strongly correlate with mortality at the neighborhood level. For the elderly and those with lower socioeconomic status, , deeper reservoirs of social capital are linked with lower levels of mortality.

Conclusion: While most societies invest heavily in physical infrastructure to mitigate future shocks, this paper reinforces the growing call for spending on social infrastructure to develop communities which can cooperate and collaborate during crises. For the elderly and poor, social ties can serve as a literal lifeline during times of need.