Variations in Seismic Anisotropy Across the Canadian High Arctic

English Abstract:

The Canadian High Arctic is a complex and little-studied area made up of the northern edge of the Canadian Shield plus several orogenic belts and basins. Each geological province has its own characteristics, from the NW-SE thrust fault and fold structures of Ellesmere Island to the NE-SW structures and diapirism of the Sverdrup basin. This great variation in surface geological structure likely reflects tectonic complexity at the scale of the entire lithosphere, but the role of past and present mantle processes in the development of the region is still poorly understood. One of the signatures of mantle tectonic processes is seismic anisotropy, the directional dependence of seismic wave propagation speed. This seismic anisotropy can arise from ‘fossil’ fabric in the lithosphere, related to past tectonic processes, and from present-day mineral alignments due to sub-lithospheric mantle flow. We use measurements of shear-wave splitting to investigate the anisotropy beneath the Canadian High Arctic. Our seismic data come from permanent seismograph stations (the Global Seismograph Network and the Canadian National Network) across the region, and a temporary installation on Ellesmere Island (the ‘ELLITE’ project). Data timespans range from 2 years for the temporary installations to 24 years for the longest-running permanent stations. Both SKS and SKKS waveforms are used in the analysis. Preliminary shear-wave splitting measurements, showing the dominant directions of seismic anisotropy across the High Arctic, are presented and interpreted in the context of tectonic structure and present-day mantle flow. The results show significant variability in splitting parameters across the region, including variations in fast-polarisation orientation at short spatial wavelengths. This and the correspondence between large-scale tectonic structure and fast orientation (e.g. E-W at station ALE and WNW-ESE at station RES) suggests that lithospheric anisotropy plays a significant role.