In Situ Stress Variations Associated with Regional Changes in Tectonic Setting, northeastern Brooks Range and eastern North Slope of Alaska

The northeastern Brooks Range of northern Alaska is an active, north-directed fold-and-thrust belt that is advancing on the Barrow Arch and the north-facing passive margin of the Arctic Basin. Density logs, leak-off tests and mud profiles from 57 wells from the northeastern North Slope were used to determine the magnitude of the present-day in situ stresses and document significant regional lateral and vertical variations in relative stress magnitude.

Preliminary analysis indicate two distinct stress regimes across this region of Alaska. Areas adjacent to the eastern Barrow Arch exhibit both strike-slip (S_hmax > S_v > S_hmin) and normal stress regimes (S_v >S_hmax >S_hmin). This in situ stress regime is consistent with observed fault patterns in the subsurface and with north-south extension along the Barrow Arch and the north Alaska margin.

To the south in and near the northeastern Brooks Range thrust front, in situ stress magnitudes indicate an active thrust fault regime (S_hmax > S_hmin > S_v) is present at depths up to 6000 ft. This is consistent with the fold and thrust structures observed in surface exposures and in the subsurface. However, at depths greater than 6000 ft, the relative in situ stress magnitudes indicate a change to a strike slip regime. This observation is consistent with the few earthquake focal mechanisms in the area and suggests deep north-northeast oriented strike slip faults may underlie the western margin of the northeastern Brooks Range.