In this study, we take a close look at the constituents of the Richter (1935) relation for calculation of local magnitude (), which is the basis for magnitude determination by Natural Resources Canada (NRCan) in the western Canada sedimentary basin (WCSB). Using a comprehensive catalog of Wood–Anderson amplitudes from earthquakes in northeast British Columbia and western Alberta, we first compare the distance correction terms for the Richter magnitude scale previously obtained for WCSB and several other regions. We also formulate a new correction term specifically for NRCan’s routine calculation that better accounts for the attenuation of direct and refracted waves from events within WCSB. Based on a bilinear model for ground‐motion attenuation, our is
in which is the hypocentral distance. Our results in lower by an average of 0.29, 0.27, 0.12, and 0.34 units, respectively, compared with those obtained by Richter (1958; California), Hutton and Boore (1987; California), Brazier et al. (2008; Ethiopian plateau), and Bona (2016; Italy) over all distances, but gives higher values than those obtained by Yenier (2017; WCSB), with an average of 0.12 unit over all distances. The difference between our calculation and Yenier (2017) is more significant for (0.27 unit) and varies slightly for larger : 0.08 unit for , 0.12 for , and 0.10 for .