The March 25, 1998 Antarctic plate earthquake

The March 25, 1998, Antarctic plate earthquake (M-W=8.1) occurred similar t o 250 km from the nearest plate boundary, in oceanic lithosphere with an ag e of 35-55 my. Analysis of aftershock patterns shows that the earthquake ru ptured a fault, or series of strike-slip fault segments, nearly 300 km long . The strike of the fault(s) is nearly perpendicular to the north-south tre nding fossil fracture zones which are the most marked bathymetric features of this region. Moment release during the mainshock was concentrated in two large subevents, clearly visible in the teleseismic body wave waveforms. M odeling of these body waves using a finite fault source places the first of the two subevents near the point of rupture initiation, on the eastern end of the fault, with the second large subevent occurring 220-280 km to the w est. The two pulses of moment release are found to be separated in time by similar to 65 s. Comparison of the relative S wave amplitudes of the first and second pulses suggests that a rotation of the focal mechanism by simila r to 10 degrees occurred between the two subevents.