The earthquake of November 5th, 1997 at 21:34 EST (02:34 GMT, November 6th) was centred in the western suburbs of Quebec City in the vicinity of Cap-Rouge. The proximity of the earthquake epicentre (46.80 N, 71.42 W) to the Quebec City urban area and the magnitude (5.1 on the Nuttli Magnitude Scale) combined to make this tremor strongly felt (Maximum Intensity VII). It was also felt as far away as Ontario, New Brunswick and New England. However, the focal depth of the event (22km) was probably deep enough to reduce the extent of damage at the surface so relatively few (5 or 6) cases of minor property damage were reported. An intensity survey conducted by the Geological Survey of Canada via the GSC's seismology web page (www.seismo.nrcan.gc.ca) documented over 1000 reports of shaking effects from 197 different communities in eastern Canada and the northern U.S.
The fault-slip mechanism for the event calculated with P-phase first motions from 35 seismograph stations indicates primarily a reverse-fault rupture with one nodal plane dipping steeply to the southeast (near 70 degrees) and trending N50E approximately. The mechanism is similar to those calculated for many other earthquakes in eastern Canada and especially for earthquakes in the Charlevoix Seismic Zone some 150 km northeast of Quebec City. There, there is increasing evidence that most magnitude 4+ earthquakes reactivate the Iapetan rift faults. Indeed, in the epicentral area of the Cap-Rouge earthquake, field mapping, gravity, magnetics and seismic reflection data also show clear evidence of basement 'en echelon' Iapetan faulting that is compatible with the focal mechanism derived.
An aftershock field survey was conducted in the epicentral area by the Geological Survey of Canada from November 6th to December 26th. Five different sites were occupied with 4 sets of portable seismograph instruments, recovering data for 35 aftershocks with magnitudes ranging from -0.9 to 2.9. Several of the larger aftershocks were also felt. The aftershock hypocentres located with the field data tightly cluster at 22 km depth, probably within a few kilometers of the main shock rupture.