western quebec and southern ontario - Department of Geology

striking faults is located in the south-eastern part of the Ottawa River (Figure 5.5). Therewas little information known on the seismicity of this area prior to the augmentation ofthe regional seismic network beginning in 2002 (POLARIS). The earthquakes in OttawaRiver area is divided into three clusters: WQ6, WQ7 and WQ8 (Figure 5.3).Cluster WQ6 is in the south-eastern part of the Ottawa River region from latitude44.8° to 45.3°and longitude -73.8 to -75.9°. There are 15 events in this cluster with focaldepths ranging from 12 km to 18 km. The 1944 Cornwall-Massena earthquake withmagnitude of 5.6 m N is the strongest event in this cluster (event T2). The fault plane ofthis event is oriented NNW-SSE, which is similar to the strike of most of the events inthis cluster (Figure 5.14). Most of the events have reverse type focal mechanism; some ofthem yield a small strike-slip component. There is one event of a normal type. The rosediagram for the strike of the nodal planes in this cluster shows predominantly NW-SEorientation (~ 124°-304°) but there are nodal planes striking almost N-S (~10-190°) andENE-WSW. Only the NW-SE oriented nodal planes are consistent with the faultorientation on Figure 5.5 and Figure 5.13. The dip angles of the nodal planes are smaller(~27°) in NNW direction, and vary between 41° and 48° for all other deractions. Thereare some nodal planes with dip angle around 71° (in N direction).WQ7 is located in the northern part of the Ottawa River region from latitude 45.5to 46.15°and longitude -74.9 to -77.7° with 12 events. The Focal depths of the events aremainly between 16 km to 26 km. The 2010 Val-de-Bois earthquake (m N 5.7) is thestrongest event in this cluster. Most of the events have reverse type focal mechanisms.There are a few events of predominant strike-slip type. The strongest event here and mostother events have NW-SE strike (~124°-304°) (Figure 5.15b). This orientation is85