Using Comprehensive Science-based Disaster Scenarios to Support Seismic Safety Policy: A Case Study in Los Angeles, California

Abstract:

In 2014, the USGS entered a technical assistance agreement with the City of Los Angeles to apply the results of the 2008 ShakeOut Scenario of a M7.8 earthquake on the southern San Andreas fault to develop a comprehensive plan to increase the seismic resilience of the City. The results of this project are to be submitted to the Mayor of Los Angeles at the Great ShakeOut on October 16, 2014. The ShakeOut scenario detailed how the expected cascade of failures in a big earthquake could lead to significant delays in disaster recovery that could create financial losses that greatly exceed the direct losses in the event. The goal of the seismic resilience plan is to:

• protect the lives of residents during earthquakes
• improve the capacity of the City to respond to the earthquake 
• prepare the City to recover quickly after the earthquake so as to protect the economy of the City and all of southern California

To accomplish these goals, the project addresses three areas of seismic vulnerability that were identified in the original ShakeOut Scenario:

1. Pre-1980 buildings that present an unacceptable risk to the lives of residents, including “non-ductile reinforced concrete,” and “soft-first-story” buildings
2. Water system infrastructure (including impact on firefighting capability)
3. Communications infrastructure

The critical science needed to support policy decisions is to understand the probable consequences to the regional long-term economy caused by decisions to undertake (or not) different levels of mitigation. The arguments against mitigation are the immediate financial costs, so a better understanding of the eventual benefit is required. However, the direct savings rarely justify the mitigation costs, so the arguments in favor of mitigation are driven by the potential for cascading failures and the potential to trigger the type of long term reduction in population and economic activity that has occurred in New Orleans since Hurricane Katrina.