SEISMIC ACCELERATION ZONES IN THE VANCOUVER AREA

Since 1990, an increased number of locations for the Lower Mainland of British Columbia has been listed in the Table of Climatic Data in the Supplements to the National Building Code of Canada. While for most o f the new locations the seismic acceleration and velocity zones are sh own as Z(a) = Z(v) = 4, Ladner is listed with Z(a) = 5, leading to sig nificant cost increase in the construction of certain types of buildin gs. Although the zonal value is formally correct, it is suggested that such discrimination is not justified by the current precision of seis mic hazard estimation. The Canadian National Committee on Earthquake E ngineering does not address regional variances of this nature; it is, therefore, further suggested that a regional committee should decide o n an equitable solution, with due consideration of estimated probabili ties of exceeding ground motion parameters, and the precision of these estimates. Some of the background and details aiding such a decision arc discussed.