Lessons learned from dynamic analyses of Mexico City and applied to Richmond B.C.

The implications of the acceleration data recorded during the September 19, 1985 Mexican earthquake for seismic design in Canada are investigated by determining if the deep deposits of the Fraser Delta could cause large amplification of earthquake motions. The conditions for amplification of low level incoming ground motions at deep sites are identified; in particular, the critical role of variation in shear modulus with shear strain. The current procedure for determining site specific ground motions is evaluated and major sources of uncertainty in the results identified. Criteria for selecting representative input motions for site response studies are recommended based on analyses of Mexico City sites. A comparative study of sites in the Fraser Delta area of British Columbia showed that offshore subduction earthquakes should be considered when developing design spectra for deep sites in the Delta.Applied Science, Faculty ofCivil Engineering, Department ofGraduat