The goal of this research is to investigate how high-rise buildings may perform in large subduction earthquakes. This includes giant earthquakes (Mw>9) such as are expected on the Cascadia subduction zone. Unfortunately, strong ground motions have never been recorded from such events, although they are expected to be rich in long periods and have long durations. Currently, the M 8.3, 2003 Tokachi-Oki earthquake is the largest well recorded subduction earthquake; 276 high-quality strong motion records are available from Hokkaido Island for this event. This research team has analyzed these 276 ground motion recordings and has simulated their importance to 6- and 20-story steel moment-frame buildings that were designed according to the 1994 Uniform Building Code. Although there were no such buildings in the strongly shaken regions of Hokkaido, these simulations indicate that if there had been high-rise buildings, then they would have been strongly excited throughout the coastal region, with the potential for collapse in some locations. The primary focus of this 2-year research project is to extend the existing work on the Tokachi-Oki earthquake to infer the performance of high-rise buildings in even larger magnitude earthquakes. It is proposed to use the empirical Green's function technique to simulate a M 9 earthquake on the Cascadia subduction zone. Using the 2003 Tokachi-Oki earthquake as source of Green's functions, the research team will simulate both strong motion and teleseismic body waves for the 2004 Sumatran earthquake (M 9.2). Careful attention will be given to the amplification of long period waves in the Seattle basin. Simulated ground motions will be used as inputs to the nonlinear analysis of steel frame buildings. This study should provide an assessment of current the adequacy of current design procedures used for high-rise buildings in the Pacific Northwest.
