Seismic Activity in the Northern Ontario Portion of the Canadian Shield

The apparent rate of occurrence of smaller earthquakes will vary, however, as the magnitude of the smallest locatable event (magnitude of completeness) of the seismograph network changes. [...] The number of stations and the number of earthquakes detected are tabulated in Table 2 since 2000 and plotted in Figure 3 since 1980, just before the inception of the northern Ontario seismic program in 1982. [...] After declustering, some of the variability of yearly occurrence rates of earthquakes of all magnitudes will be due to the intrinsic randomness of the underlying process, but some of it will be due to changes in the magnitude of completeness of the network. [...] The event is assigned to the location of the larger, well-located event, and then the available seismograph readings are used to determine the origin time and magnitude of the aftershock. [...] In addition, as the size of the event decreases, the number of stations that clearly record that event will decrease, and the onset of the phases will become less clear.