Characteristics of Shear Wave Velocity Structures Beneath the Gulf of St. Lawrence, Eastern Canada from Ambient Seismic Noise Tomography

Continuous ambient seismic noise waveforms collected from 2005-2008 at 24 broadband stations located in and around the Gulf St. Lawrence (GSL) are processed to derive Rayleigh wave dispersion curves. We conduct both surface wave tomography inversion and trans-dimensional Bayesian inversion to characterize the 3-D shear wave velocity (Vs) structure beneath the GSL up to 20 km depth. Our results indicate that the entire GSL region can be divided into three broad sections. In the northern GSL, the Grenville Province (i.e., the Proterozoic edge) is dominated by high Vs. However, scattered low Vs structures can be found to correspond to well-known anorthorsite sites. In contrast, the central section corresponds to a weak belt with generally low Vs. The southernmost section of the GSL is characterized by high Vs structures belonging to the Meguma and Avalon terranes. The basement structure at the eastern segment of the Appalachian Structural Front is characterized by relatively low-Vs. Prominent low Vs are found to coincide with locations of most graben structures and sedimentary basins in the GSL. Both the depth of the sedimentary basement and the geometry of major sedimentary basins are well imaged with the thickest sedimentary layer (over 15 km) found near the western edge of the Magdalen basin. At both shallow and mid-crust depths, prominent high Vs are found near the boundaries of the Ordovician-Silurian Anticosti and the Carboniferous Magdalen Basins. The deepest prominent low Vs structures correspond to displaced/deformed Humber zone sediments buried deep beneath Dunnage zone of Newfoundland. High Vs structures with variable thicknesses are found to overlie parts of the Canadian Maritime Basins. These top high Vs structures are generally very thin (<3 km) and can be explained as the manifestation of top volcanic layers in the region.