Seismotectonics of the Beaufort Sea

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Abstract
Earthquake data are utilized in conjunction with bathymetry and gravity measurements to study the seismotectonics of the Beaufort Sea area. The epicentre cluster in the Beaufort Sea is confined to the continental slope between the 200 and 2400 m bathymetry contours and falls between the seaward −20 mGal and the landward + 40 mGal contours of an elliptically shaped free-air gravity anomaly. The cluster, which experiences an average of one earthquake magnitude ≥ 4 per year, is shown by epicentre relocation studies to be a distinct zone and not the result of mislocations of earthquakes originating from a spatially confined source. Theoretical calculations of the stress field under the region where the gravity anomaly is most pronounced show that the horizontal component of the stress field is deviatoric tension normal to the axis of the continental margin; focal parameters of the June 14, 1975, mb 5.1, Ms 4.2 Beaufort Sea earthquake indicate deviatoric tension in the same (east–west) direction at a depth of 40 km. The relatively small surface waves from this and other Beaufort Sea earthquakes, compared to other on-shore Arctic earthquakes, are probably due to this deeper focus at the continental margin. The horizontal component of the deviatoric compression of this earthquake is north–south; a horizontal compressive stress from the north may be transmitted through the Arctic Ocean lithosphere from the Nansen–Gakkel spreading ridge. It is suggested that these stresses are acting on localized zones of weakness.

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