Paper No. 199-13
Presentation Time: 11:20 AM
IS SEISMICITY IN THE WESTERN QUÉBEC SEISMIC ZONE DRIVEN BY GLACIAL REBOUND?
Much of the ongoing seismicity in eastern Canada is attributed to the recession of glacial ice sheets at ~10-20 ka. Crustal rebound following ice sheet recession has resulted in a finite interval of increased seismicity in a thrust-regime crustal stress setting. As the rebound effects subside, seismicity is expected to decrease. The western Québec Seismic Zone (WQSZ), which encompasses the region from Ottawa to Québec along the Lower St. Lawrence River and north to the Abitibi area, is one of the most seismically active zones in Canada. Although generally attributed to rebound effects or far-field tectonic stresses, the causes of seismicity in this area have never been directly tied to any forcing mechanism due to a lack of geodynamic modeling of the region and a dearth of identified active faults. Though it is widely assumed that ongoing seismicity is associated with crustal rebound-driven reactivation of late Proterozoic to early Paleozoic Iapetan rift structures, this assumption has not been confirmed by neotectonic fault studies, and the region of active seismicity does not coincide with the known structures. We use a revised focal mechanism dataset from the WQSZ to drive analysis of a recently released set of 1 m-resolution lidar-derived digital elevation models covering the whole of the WQSZ. The release of this lidar dataset allows us an unprecedented opportunity to identify scarps within the WQSZ that, with future detailed field studies, may be related to post-glacial faulting. Inspired by work in Fennoscandia, we are in the process of adapting methods for distinguishing possible faults from the geomorphic effects of ice flow and recession. We discuss successes and challenges we've encountered in this preliminary work thus far and our ongoing efforts to determine a set of Québec-specific identification metrics for active fault structures. This will lead to a dramatically improved understanding of the shaking hazard posed to the major Canadian cities that lie within the WQSZ, such as Ottawa, Toronto, and Montréal, as well as our neighbors across the United States border.