Discussion: Engineering applications of new probabilistic seismic ground-motion maps of Canada

Abstract

Listen

Translate article

Concerning the development of the earthquake design requirements of the National Building Code of Canada (NBCC) starting from 1956, the authors state Uzumeri et al. (1978) have described these and subsequent developments in NBCC seismic loading provisions up to the 1977 edition of the code (p. 671). This paper contains erroneous references to the 1970 edition of the NBCC and its Commentary No. 3, Earthquake loads (Ferahian 1970) as pointed out in my discussion of the paper (Ferahian 1979). For historic authenticity, if for nothing else, it should not have been quoted without simultaneously referencing the discussion. In the development of the 1970 seismic regionalization map (authors' Fig. 1 ), the parameter chosen was A , , , the seismic ground acceleration with an annual probability of exceedance of 1 in 100, corresponding to the earthquake with a 100 year return period. Apart from the reasons given elsewhere (Ferahian 1970, 1979), this earthquake was chosen because the instrumental recording of our earthquakes does not predate the turn of the century. Estimates were made for the A,, and A,, seismic ground accelerations but because of the uncertainties inherent in the study, only the former were given in Commentary No. 3 for some representative cities in Canada. It was believed then that the confidence limits in these estimates were such that even the A , , estimates could be out by a factor of 2 (Ferahian 1970), and the corresponding factor would be much higher for A 500 For the seismic regionalization maps of Canadaadopted for the 1985 NBCC-the authors have used the earthquake with a 10% probability of exceedance in 50 years, which for all practical purposes corresponds to the 500 year return period earthquake. They claim, without giving proof, that their estimates of the peak seismic accelerations and velocities corresponding to