Physical characterization of seismic ground motion spatial variation and conditional simulation for performance-based design

Abstract

The spatial variation of seismic ground motions is critical for the response of lifeline structures, such as bridges and dams. The physical characterization of the seismic spatial variation and the realistic simulation of the spatially variable ground motion random field become then vital to the success of performance-based design of these extended structures. To obtain insight into the physical properties of spatial variation, extensive analyses of recorded time histories at selected seismic dense arrays are carried out herein. First, the spatial variation at the Parkway valley, New Zealand dense instrumental array is analyzed on the basis of two recorded events. The variation pattern of the seismic coherency due to wave types, station pair orientations and site conditions, together with the possible significances for engineering practice, are investigated. Next a physical methodology to characterize seismic ground motion spatial variation is further validated by six events with different magnitudes and source mechanisms recorded at five arrays with different configuration and site conditions. The results indicate that there exists a correlation pattern between amplitude and phase spatial variability for the six diverse events. This interesting observation renders the possibility to associate the spatial variation with physical parameters and simulate seismic ground motions compatible with recorded data. A conditional simulation scheme for the performance-based design of extended structures is thoroughly analyzed. Issues concerning the proper processing of simulated acceleration time histories to yield realistic velocities and displacements are addressed for the first time. Near-field and far-field spatially variable ground motions are generated as applications of the approach.%%%%Ph.D., Structural Engineering – Drexel University, 2006