western quebec and southern ontario - Department of Geology

ecorded within this cluster. As it can be seen from Figure 5.21, most of the events haveoblique-slip focal mechanisms. The dip angles of the nodal planes in this cluster are 38°to 58° in NW-SE direction and 34° to 71° in NE-SW direction (Figure 5.21c). Thepressure axes varies from E-W to EES orientations. (Figure 5.21d), similar to thenortheast strike of the boundary zones dividing the main tectonic segments of theGrenville province (the GFtz, CMBbtz, and EFbz) (Easton, 1992). Seismicity in thisregion is compatible with reactivation of pre-existing fault zones in this zone (Figure 5.20).A comparison of the strike of the nodal planes for all clusters in the study area andthe known tectonic features is shown in Figure 5.22. As discussed in details the generalaverage strike of focal mechanisms of the events in southeastern part of the WesternQuebec seismic zone is N-S, which is compatible with the faults and other pre-existingshear zones in this area. For the rest of western Quebec, the strike of the focalmechanisms is generally in NW-SE direction, which is also compatible with local faultsand structures in most cases, as discussed above. For southern Ontario, the strike of thefocal mechanisms of the events is mostly in N-S to NE-SW. This is consistent with thedirection of major shear zones in this area. As the structural dip can affect both the depthand epicentres of the earthquakes they may line up on the surface but not at depth. Forcomparison of the hypocentre locations with the faults in depth there will be necessary tohave more high-quality hypocentres. This discussion is based on a limited number ofearthquakes studied here, and more detailed analyses with larger earthquake database isrequired to define if there is a correlation between the hypocentre locations and the faults.96