Geoscience Reference
In-Depth Information
Figure 4.3 (a) Earthquakes of magnitude
1.0 recorded between 1978 and 2012 in the CSZ. The
estimated position of the 1925 earthquake's epicentre and assumed fault plane orientation is shown as
a red ellipse. The semi-circle of the Charlevoix meteorite impact crater is clearly visible on this image,
where topography is shown using colours that range from blue for the lowest elevations to red for
the highest ones. Since 1978, earthquakes have been monitored by a network of seven seismographs
(white triangles).(b) Idealized cross-section perpendicular to the St. Lawrence River in the CSZ.
The earthquake activity occurs in response to ridge push stresses (arrows) and is constrained to the
Canadian Shield rocks, beneath the St. Lawrence River (SLR), St. Lawrence platform rocks (in grey),
Logan's Line, and the Appalachian rocks. The 1925 earthquake ruptured along one of the large SLRS
faults at focal depth of about 10 km at the extremity of the CSZ. A small proportion of earthquakes
occur within the Charlevoix Meteor Impact Structure (MIS). Earthquakes tend to concentrate outside
