Linear zones, seismicity, and the possibility of a major earthquake in theintraplate western Lake Ontario area of eastern North America

Seismic hazard assessments conducted in eastern Canada rely on seismologica l data, which are essential, but alone, inadequate. That is because the ear thquake record is too short to provide a representative picture of where la rge 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 li neaments were investigated and the results were combined with available sei smological information. The most conspicuous is the Niagara-Pickering linea r zone, within which there have been at least two, if not three, periods of brittle faulting, including displacements compatible with the current stre ss field. It also appears to represent the same major structure as the Akro n magnetic boundary in eastern Ohio, the site of the m(b) = 4.9 Leroy earth quake. The second is the Georgian Bay linear zone, which extends from Georg ian Bay to New York State. It displays evidence of recent outcrop-scale fau lting, an alignment of earthquakes along its southwestern boundary, and a p ossible spatial relationship to other earthquakes, including two of M great er than or equal to 5. Lastly, there is the Hamilton - Lake Erie lineament, which is parallel and proximal to a possible fault and coincides with a li near array of small to moderate earthquakes. All three converge on the west ern Lake Ontario area, which has a higher frequency of seismicity than the adjacent areas. Thus, the western Lake Ontario area might have a greater po tential to experience a major earthquake than heretofore believed.