Contemporary reverse faults, marked by offset boreholes, were identified in two roadcuts, and recently formed pop-ups, which are surficial chevron folds, have been recognized in a quarry in the Ottawa-Hull area of Ontario and Quebec, Canada. Displacement directions of the hanging walls, marked by the offset boreholes, are commonly north-northeast to east-northeast, though one set shows displacement to the northwest. The pop-ups recorded during this investigation show average orientations of 120 and 063°. These are similar to the average trends of 136 and 074° documented in a previous study from a quarry about 20 km away. East-southeast- to southeast-trending pop-ups predominate in the two quarries and are kinematically compatible with most of the offset borehole directions recognized to date in the Ottawa-Hull area. Moreover, the quarry-floor pop-up trends in the Ottawa-Hull area are consistent with those of open field, lake bottom and other quarry-floor pop-ups in an area extending from the Miramichi region of New Brunswick into the east-central U.S.A. The compressional origin of the reverse faults and pop-ups, and the predominant orientations of those structures, are compatible with the current ambient stress field in eastern North America. This implies that both the displaced boreholes and quarry-floor pop-ups are products of that stress field, and, despite their presence in excavations, are tectonic in origin.

La néotectonique de la région des Grands Lacs Volume 47, numéro 3, 1993 URI : id.erudit.org/iderudit/032961ar

Seismic hazard assessments conducted in eastern Canada rely on seismological data, which are essential, but alone, inadequate. That is because the earthquake record is too short to provide a representative picture of where large earthquakes have occurred in the past. Consequently, seismic hazard may be underestimated in areas, such as that encompassing western Lake Ontario, that are devoid of documented large earthquakes. To attempt to ascertain the likelihood of a major earthquake occurring in that highly populated and industrialized area, three regionally extensive geophysically expressed lineaments were investigated and the results were combined with available seismological information. The most conspicuous is the Niagara-Pickering linear zone, within which there have been at least two, if not three, periods of brittle faulting, including displacements compatible with the current stress field. It also appears to represent the same major structure as the Akron magnetic boundary in eastern Ohio, the site of the mb = 4.9 Leroy earthquake. The second is the Georgian Bay linear zone, which extends from Georgian Bay to New York State. It displays evidence of recent outcrop-scale faulting, an alignment of earthquakes along its southwestern boundary, and a possible spatial relationship to other earthquakes, including two of M >= 5. Lastly, there is the Hamilton - Lake Erie lineament, which is parallel and proximal to a possible fault and coincides with a linear array of small to moderate earthquakes. All three converge on the western Lake Ontario area, which has a higher frequency of seismicity than the adjacent areas. Thus, the western Lake Ontario area might have a greater potential to experience a major earthquake than heretofore believed.

No abstract

Pop-ups, which form in response to high horizontal surface and near-surface stresses, were recognized on the floors of two quarries in metropolitan Québec City. This note constitutes the first published documentation of pop-ups in the Québec City area.The orientation of most of the pop-ups is consistent with the stress system affecting eastern North America; however, pop-ups with other orientations have also been recognized. The origin of the latter may reflect local stress conditions.