Azimuthal anisotropy of Hudson Bay 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. Using azimuthal anisotropy results in conjunction with isotropic group velocity maps from previous work, we can further focus our study on determining the formation and regional crustal structure beneath Hudson Bay. Twenty-one months of continuous ambient-noise recordings have been acquired from 37 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. The inter-station group-velocity dispersion curves found from noise-generated seismic-interferometry studies, also know as ambient-noise tomography, are input into a tomographic inversion procedure producing images of crustal azimuthal anisotropy. This study marks the first where ambient seismic-noise data have been considered in azimuthal anisotropy work. Our resolution testing suggests that the interpretation of the results requires some caution, but good path coverage is available. Preliminary results show a dominant southwest-northeast anisotropic direction, with weak correlation with the tectonic belts. In contrast, previous anisotropic studies have found that crustal anisotropy is strongly correlated with regional geology. Our results suggest that contributions from other forces may be important. Stresses, including large-scale regional stresses from plate motion are considered, but also show little correlation with our data. Local glacial isostatic rebound may be a contributing factor, but further work is required.