Source time function complexity of the great 1989 Macquarie Ridge earthquake

The rupture process of the great 1989 Macquarie Ridge (M_w = 8.1) strike-slip faulting earthquake is examined using an empirical Green function deconvolution method which provides broadband source time functions from both body and surface waves. Recordings from a nearby, much smaller (M_w = 6.4) strike-slip event provide accurate broadband Green functions for PP, S, SS, Rayleigh, and Love waves, spanning the period range 20-150 s. Body wave deconvolutions indicate that the principle short-period (<30 s) moment release occurred in the first 25 s of rupture with no resolvable directivity; only minor short-period energy release occurred over the next 30 s. Surface wave deconvolutions for the usually neglected 20-150 s period range produce source time functions with slightly larger total moment than the body wave deconvolutions and no resolvable directivity from the onset to the peak of moment release in the first 20 s. However, azimuthally dependent broadening of the surface wave source functions indicates a component of northeastward unilateral rupture extension requiring about 30-50 km asymmetry in the overall rupture, compatible with the northeastward asymmetry of the 1-day aftershock zone. -from Authors