Re-visiting the tectonics of the oceanic intraplate earthquake of March 25, 1998 (M 8.1) in the Balleny sea, offshore Antarctica

Abstract

The Antarctic plate earthquake of March 25, 1998, M 8.1, and its aftershocks, are re-visited, to evaluate the role of the associated tectonics in stress concentration due to ambient horizontal crustal motion caused by deglaciation in Antarctica. Using a numerical technique called the “Distinct Element Method”, a two-dimensional, structural model of the epicentral region is developed, and tectonically loaded for a year along the inferred direction of the motion. A spatial correlation is observed between the resulting locations of relatively high shear stresses, and those of the main shock and associated aftershocks. In particular, seismicity is concentrated at and near the intersections of the main fault, Carey and Gambier fracture zones, where the shear stresses are significantly elevated, and whose sign duplicate the inferred sense of movement along them. The modeling results suggest that stress concentrations near pre-existing, intersecting fault and fracture zones, due to a possible deglaciation induced horizontal crustal force, may have been a cause of this enigmatic earthquake.