Earthquakes and geological structures of the St. Lawrence Rift System - Intraplate Earthquakes - page 78

Figure 4.2 Seismicity of the SLRS in southern Quebec and eastern Ontario. Earthquakes of magnitude
larger than 3.0 recorded between 1980 and 2012 inclusively together with significant earthquakes of
Eastern Canada are shown (listed in Table 4.1 ; Lamontagne et al ., 2008a ) . Seismic zones are: WQSZ
, Western Quebec Seismic Zone; CSZ, Charlevoix Seismic Zone, as defined by Basham et al .( 1982 ) .
Other acronyms are: GMHST, Great Meteor HotSpot Track (assumed); OBG, Ottawa-Bonnechere
Graben; SG, Saguenay Graben; LL, Logan's Line. Place names are: TOR, Toronto; OTT, Ottawa;
MTL, Montreal; QC, Quebec City; TR, Trois-Rivieres; T, Temiscaming. Rivers and lakes mentioned
in the text are: LT, Lake Temiscaming; OR, Ottawa River; SMR, Saint-Maurice River; SR, Saguenay
River; SLR, St. Lawrence River. For colour version, see Plates section.
earthquake. Its effects included liquefaction and rock falls in the epicentral region and land-
slides as far as 200 km from the epicentre. At 30 km from the epicentre, for example,
liquefaction caused extensive damage to local houses (Lefebvre et al ., 1991 ; Boivin, 1992 ) .
There, evidence of older liquefaction and ground failure was found, possibly caused by
older regional earthquakes (Tuttle et al ., 1990 ) . Other damage was seen as far as 170 km
away from the epicentre where failures of railroad embankments were reported (Mitchell
et al ., 1990 ) . Natural slope failures were also seen along the Saint-Maurice River (Lefeb-
vre et al ., 1992 ) . For building design, this earthquake was the first M 6 eastern Canadian
earthquake recorded by strong ground motion instruments and showed the high-frequency
content of earthquakes there (Munro and North, 1989 ) . In general, infrastructure in the
SLRS is especially at risk where marine clays are found, because even moderate earth-
quakes can trigger earth flows. In 2010, for example, the M 5.0 Val-des-Bois earthquake
caused two earth flows within a few kilometers of the epicentre (Perret et al ., 2011 ) .