Seismic Anisotropy Variations Across Greenland: Evidence From Shear Wave Splitting

Much of Greenland is a stable craton containing Precambrian rocks associated with the Laurentian continent. Despite the current stability of the region, Greenland's geology preserves orogenic belts and traces of ancient subduction processes dating from Precambrian to Mesozoic times. In order to find out how these deformation zones are preserved in the lithospheric mantle, we investigate upper-mantle seismic anisotropy using the method of shear wave splitting. When a shear wave meets an anisotropic medium, it separates into two orthogonal components, "fast" and "slow", aligned along, and transverse to, the orientation of anisotropy. We measure the time delay between the two waves, which depends on the thickness of the layers and the strength of the anisotropy, as well as the azimuth of the fast wave, which aligns with the preferential direction of deformation of the medium.

We use SKS and SKKS phases from large (magnitude >6) earthquakes from distant (>80°) earthquakes recorded at 28 seismograph stations distributed across Greenland. The recording period covers the period 1999-present, with at least 6 years of operation for the majority of the stations.

The resulting anisotropy measurements will allow a comprehensive study of variations of seismic anisotropy across Greenland. We will compare the results to previous geophysical studies, to regional tectonic trends, and to mantle geodynamic models in order to determine the source of the anisotropy; does it record ancient lithospheric deformation, present-day mantle flow, or a combination of these processes?