Ella Goldberg

Stress patterns were analyzed in parts of Atlantic Canada to determine the tectonic regimes and whether reactivation of older faults could cause damage near Point Lepreau, New Brunswick. Point Lepreau is home to a nuclear power plant and seismic risk information in the Northern Appalachians is scarce and out of date. To put this information in perspective regionally, the study area extends from south of Grand Manan Island in the southwest to the Grand Banks of Newfoundland in the northeast.

This study investigated published focal mechanism data for earthquakes from ~1970 to 2011 in the study area. Five main regions of seismicity are the Northern Appalachians, Charlevoix, Lower St. Lawrence, offshore Nova Scotia and the Grand Banks. Earthquake and focal mechanism data were obtained from the Global Centroid Moment Tensor Catalogue (1976-present), the Canadian Earthquake Database, and the U.S. Geological Survey/ National Earthquake Information Centre database (1973-present) and focal mechanism data from several Geological Survey of Canada open files. Focal mechanism information is scarce for most regions. In order to better characterize the principal stress pattern for the regions, the World Stress Map Data (2008) were included in the study. The only event that had a known fault plan was the 1929 Mn= 7.2 Laurentian Slope event that caused a submarine slump which then induced a tsunami (Bent, 1995).

Analysis of focal mechanisms showed thrust-fault stress regime in the Gulf of St. Lawrence with three clusters of principle compressive stress axes where two clusters are separated by the St. Lawrence fault. Some of the Northern Appalachian's focal mechanisms show strike-slip stress regime. Between the Bay of Fundy and the Gulf of St. Lawrence, World Stress Map data show thrust faulting with a strike-slip component closer to the Northern Appalachians and pure thrust faulting closer to the Gulf of St. Lawrence. In the Grand Banks region, stress orientations seem random and the cause of earthquakes is unknown. Offshore Nova Scotia, the stress orientations seem to coincide with the trend for North America and are compatible with the extension perpendicular to the passive Atlantic boundary.

Shear stress on two major faults was calculated; the St. Lawrence Fault in the Charlevoix region and the Oak Bay fault in the Northern Appalachian region. The shear stress on the Oak Bay fault was found to be very small and reactivation is unlikely while some faults in the Charlevoix region are oriented the same as the St. Lawrence fault; indicating that reactivation happens occasionally.

In summary; the Oak Bay fault is an unlikely threat to Point Lepreau's nuclear power plant, the Charlevoix region's St. Lawrence fault is active but the largest threat to Point Lepreau are earthquake-induced tsunamis or earthquake-induced landslides that can generate tsunamis in the Laurentian Slope zone.

Pages: 73
Supervisor: Djordje Grujic