Imaging the Hudson Bay basin using seismic interferometry

Agnieszka Pawlak, David W. S. Eaton

The Hudson Bay basin is the least studied of the four major Phanerozoic intracratonic basins in North America, which include the hydrocarbon-rich Williston, Illinois and Michigan basins. This study focuses on regional crustal structure based on ambient-noise tomography, a recently developed passive seismic method. Twenty-one months of continuous ambient-noise recordings were acquired from 31 broadband seismograph stations that encircle Hudson Bay. These stations are part of the Hudson Bay Lithospheric Experiment (HuBLE), an international project that is currently operating more than 40 broadband seismograph stations around the periphery of Hudson Bay. Following established processing procedures that include trace normalization and spectral whitening, cross-correlations were computed for all possible station pairs. The resulting waveforms are treated as Green's functions, from which group-velocity dispersion measurements can be made. Since Hudson Bay freezes during winter months, there is a pronounced asymmetry to the Green's functions indicative of seasonal variations in noise sources, and an apparent predominance of sources from the Atlantic seaboard. Preliminary results indicate shield-like conditions in most areas, with higher velocities beneath the oldest regions, the Archean Superior craton south and east of Hudson Bay. With this exception, the upper crust beneath the Hudson Bay basin is indistinguishable from surrounding shield areas. This characteristic differs from basins in southern California that have been studied using this method and may help to constrain models for formation of the Hudson Bay basin.