Multi-Hazard Mitigation Plan: 07. Earthquakes

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Chapter 7:Hazard Analysis—Earthquakes floor of a house to provide additional lateral strength and stiffness to the foundation system. This retrofit is applicable in all regions with most combinations of differential post height and other structural properties. Retrofit Option 3 uses masonry shear walls to provide additional lateral strength and stiffness. This option is applicable for any post and pier house, although in some extreme cases a structural engineer would need to be consulted if the properties of the house fall outside the range of properties considered in the report. 7.5.1.4 Kiholo Bay HAZUS model validation and inventory update The 15 October 2006 moment magnitude (M) 6.7 earthquake beneath Kiholo Bay was among the largest to have occurred in Hawaii since written records have been maintained. For many, the Kiholo Bay earthquake served as an introduction to the fact that Hawaii is seismically active, and it reminds us that Hawaii is exposed to significant seismic hazard. Although no deaths or serious injuries were reported, damage estimates exceeded $200 million, resulting in the declaration of a major disaster by the U.S. government (FEMA- 1664-DR-HI). Development of the HAZUS (Hazards U.S.) earthquake model began in 1992 and much of the methodology is based upon empirical observations from past damaging earthquake events. There is a critical national need to document the performance of loss estimation methodologies such as HAZUS and the 2006 Kiholo Bay earthquake disaster provided a unique, but perishable opportunity to compare HAZUS-MH modeled results to those observed in the disaster. In addition, this was a relatively rare opportunity to test the model performance outside of California. The results of the validation study were also used to develop a recommended procedure for using HAZUS-MH in future events with the enhanced data to support FEMA and the State of Hawaii that addresses uncertainty and identifies the priority HAZUS-MH products. At the time of the 2006 earthquake, the State of Hawaii utilized HAZUS 99 runs with progressively more information during the first 10 hours of the quake. The runs included a 2000-vintage building inventory aggregated by census tract, developed under previous FEMA contracts for Hawaii and Maui counties. However, HAZUS 99 damage and losses far exceeded ground truthed data. FEMA, working with the USGS, obtained a rapid ShakeMap product that included ground shaking information from felt reports, as well as 12 dial-up strong ground motion stations that greatly enhanced the results of the HAZUS-MH model. FEMA completed a run using the HAZUS level 1 data and version 12 of ShakeMap on 17 October where the losses dropped to about $200M total ($30M structural). Accordingly, in this study, data improvements are made with the goal of enabling operational use of HAZUS- MH with the present-day enhanced dataset and ShakeMap, and discontinuing use of HAZUS 99. This study further enhanced the Hawaii and Maui County building stock by using residential and commercial property tax databases and several state government property databases, and conducted loss estimation at the detailed census block level rather than at the geographically large census tracts that characterize the Big Island. The project incorporated the unique Hawaii building types including the vulnerable post and pier single-wall construction type that statistically exhibited much higher damage levels than conventional wood-frame construction on slab-on-grade. 7-21 Hawaii Countv Multi-Hazard Mitigation Plan