The 1998 Antarctic intraplate earthquake (Mw8.1) has a significant non-double-couple component in the moment tensor solution as determined from long-period surface waves. In the teleseismic P and SH waveforms, there are two distinctive wave packets that can be explained by multiple strike-slip subevents. We propose a composite rupture model comprising two different episodes: two predominant clusters of en echelon strike-slip segments (~16e20Nm) and normal faulting with a long duration of approximately 100 s (~4e20Nm). This model agrees with observations of both teleseismic body waves and long-period surface waves, including the large non-double-couple component. The normal faulting with as long a duration as the main strike-slip rupture might be secondarily induced by the en echelon segments of strike-slip faulting.