western quebec and southern ontario - Department of Geology

estricted to western Lake Ontario or along the Ottawa river and along the Ohio-Pensylvania border within a cluster south of Lake Erie.• The focal depth for all earthquakes in the study area is less than 30 km. The focaldepth of the Western Quebec events appears greater than that of the SouthernOntario seismic zone. All 16 events in southern Ontario occurred at shallowdepths less than 19 km. The western Quebec events, however, are generallydeeper, with depths from 18 to 30 km. The median depth of events is 8.2 km forthe southern Ontario seismic zone and 20 km for western Quebec seismic zone.• Among the 50 events studied, 29 are thrust fault events and 21 have focalmechanisms that are predominantly strike-slip with a small component of dip-slipmovement. In terms of regional distribution, almost all events in the WQSZ havea reverse-sense focal mechanism with some spatial variability in the nodal planeorientation. Events in southern Ontario and more specifically in Lake Ontario andsouth of Lake Erie are mainly of strike-slip character. The dipping angle of thenodal plane in Western Quebec varies around 45° towards NE-SW, but inSouthern Ontario it is around 50° towards NW-SE.• The average orientation of the compression (P) axes for western Quebec wasfound to be almost NE-SW and for southern Ontario NW-SE, which areconsistent with previous studies.• Investigation of such parameters as density of the epicentres, focal depths, andtype of the focal mechanism as well as tectonic setting in both the western Quebecand the southern Ontario suggest some distinct seismic clusters. Using a simplestatistical approach (Dineva et al. 2004; Ma and Eaton, 2007), nine distinct100