The
Ottawa-Bonnechere Graben (also known as the
Ottawa Graben), is a seismically active structure that coincides with a wide topographic depression extending from near Montréal through Ottawa. It is part of the St. Lawrence rift system that also includes the seismically active Saguenay graben. This rift valley was formed when the Earth's
crust moved downward about a kilometre between two major
fault zones known as the Mattawa and Petawawa faults. These ancient faults are still active and occasionally release stress in the form of
earthquakes, such as the
1935 Timiskaming earthquake and the
2000 Kipawa earthquake. The length of the graben is about .