western quebec and southern ontario - Department of Geology

oundaries of the Central Metasedimentary Belt. There is no obvious concentration ofearthquake epicentres northwest and southeast of the western Quebec seismic zone(Figure 5.4). A similar relative absence of earthquakes is also present in the historicaldata (1627-1984) (Figure 3.1). Similarly, in the southern Ontario region most of theearthquakes appear to be clustered either around the region of eastern Lake Erie, westernLake Ontario or along the Ottawa River (Figure 5.4).Detailed investigation in the trend of epicentres in both the western Quebec andthe southern Ontario suggests some distinct seismic clusters (e.g. Ma and Eaton, 2007;Dineva et al. 2004). However, trends in earthquake epicentres alone are not enough eitherto establish seismic zones or to rule out the existence of seismic zones. Similarly, seismiczones cannot be defined solely on the basis of past geologic history of the region (Yangand Aggarwal, 1981). In fact, a combination of seismic parameters and geologicalpatterns should be used to identify and isolate those parameters that may influencepresent-day earthquake processes in the region. Dineva et al. (2004) and Ma and Eaton(2007) have developed a simple statistical approach to characterize the spatial clusteringof seismicity. The method is implemented by subdividing the area of interest into squarebins and counting the number of events that fall within each bin. An attempt is made inthis thesis to recognise potential seismic clusters in both the western Quebec and thesouthern Ontario by means of the earthquake parameters and geological features in theregion. This classification is based on earthquake parameters such as epicentre locations,focal depth, focal mechanism solutions, the pressure and tension stress directions (P- andT-axes) inferred from focal mechanism solutions, and specific lineaments inferred fromgeologic data such as faults.68