• The empirical relationship between moment (Mw) and local (ML) magnitudes is examined for small events in western Alberta. A comparison of the two magnitude scales indicate that ML attains smaller values than Mw for Mw<3. The magnitude discrepancy between the two scales increases with decreasing event size, which is in agreement with the recent findings of others (Ross et al., 2016; Munafò et al. 2016). Source spectra of small events typically attain a corner frequency well above the corner frequency of attenuation effects, which effectively suppress the contributions from spectral plateau on peak amplitude and result in ML values smaller than Mw