Ground motion estimation for evaluation of levee performance in past earthquakes

Levees provide vital functions for water delivery and flood protection. However, they present unique challenges for seismic design because their great length makes engineering evaluation of stability at closely spaced regular intervals impractical. Accordingly, relatively broad, empirically-driven risk assessment tools have the potential to serve as effective screening tools. We are undertaking a large data collection and synthesis effort to support the development of such tools, with the initial focus being on levee performance from the 2007 Mw6.6 Niigata Chuetsu-oki earthquake in Japan. Naturally, ground shaking is a key variable in this process, so the reliable estimation of ground shaking hazards fromseismic networks is an essential element of the case history analysis. We postulate thatdirect application of Krigingtechniques can produce biased ground motion estimates due to variable site conditions. Accordingly, we apply Kriging to residuals of ground motion prediction equations (GMPEs), which remove the average site effect. The resulting maps of residuals can be readily applied with the GMPE to produce ground motion maps that properly reflect spatial variations of geologic conditions.The proposed procedure produces ground motions near levees that are lower in some areas than those produced bydirect Kriging