Structure and Anisotropy of the Crust and Upper Mantle Along the St. Lawrence Corridor, Eastern Canada, From the Charlevoix Seismic Zone to the Gulf of St. Lawrence

Date: 4/25/2019

Time: 02:00 PM

Room: Pike

The St. Lawrence corridor in eastern Canada comprises three active seismic zones separated by regions of low seismicity. Understanding the unequal distribution of seismicity has potential implications for hazard assessment of this highly populated region and its critical infrastructure. Despite its intraplate setting, the region is tectonically complex. The St. Lawrence River, underlain by the St. Lawrence Platform, delineates much of the boundary between the Canadian Shield to the north and the Appalachians to the south. To better define the structural complexities of this important region, shear wave velocity models were derived from teleseismic receiver functions for seismograph stations along the St. Lawrence. Gaps in the broadband coverage of the Canadian National Seismograph Network were supplemented by temporary stations deployed for this project and by taking advantage of any other deployments in the region. The current study focuses on the region between the Charlevoix Seismic Zone and the Gulf of St. Lawrence, complementing previous work that covered the region between Charlevoix and Montreal. All stations modeled show a high velocity lid to a depth of ~5km and a Moho at 38-45 km. The structure is consistent from one station to the next. Discontinuities can be correlated allowing for the development of a pseudo-3D model. Evidence for mantle anisotropy is obtained from SKS splitting. Fast-polarization directions are subparallel to the strike of the St. Lawrence valley in the study region and parallel to the valley further west, with a slight rotation of fast orientation from west to east. The average delay time of ~1 second requires an upper-mantle component, which is likely a combination of contributions from “fossil” lithospheric anisotropy and mineral alignments from present-day sublithospheric mantle flow.

Presenting Author: Allison L. Bent

Authors