western quebec and southern ontario - Department of Geology

eastern Canada with earthquake frequency of about 50-100 events per year withmagnitude predominantly less than 5 m N . Lamontagne et al. (2003) proposed that mostearthquakes in this zone occur beneath the St. Lawrence River at focal depths betweenabout 7 and 25 km, well within the Precambrian shield. The trend of the normal faults inthe LSZ zone seems to be east-west. Lamontagne et al. (2003) have also suggested thatlocal faults in this zone could be weak due to crustal fluids at depth, probably underhydrostatic pressure, which leads to a lower internal friction.2.3.4 Southern Ontario Seismic ZoneThe Southern Ontario Seismic Zone includes Southern Ontario and the areas just south ofLake Erie and Lake Ontario. This is a zone with low to moderate earthquake activity.Moderate seismic events such as the 1986 Cleveland, Ohio earthquake with a magnitudeof 5 m N , the 1929 Attica earthquake with a magnitude of m N 5.2, and the 1998Pymatuning earthquake with a magnitude of m N 5.4 (Armbruster et al., 1998) occurred inthis zone (Figure 2.5). Strong seismic events with magnitudes above 6 have not beenrecorded or felt since 1800 (Stevens, 1994). On average, 2 to 3 per year earthquakes withmagnitude 2.5 or larger have been recorded in this region from 1984 to 2011 (NaturalResources Canada).The seismicity in this area is mainly associated with normal faults (Adams &Basham, 1991; Adams 1995). Excluding the Ottawa River area, seismicity focusesprimarily in clusters south of Lake Erie and around western Lake Ontario. Some of thelocalized clusters include the western Lake Ontario Zone (Seeber and Armbruster, 1993),also named the Burlington-Niagara Falls cluster (Adams & Basham, 1991); the Attica19