SOURCE TIME FUNCTION COMPLEXITY OF THE GREAT 1989 MACQUARIE RIDGE EARTHQUAKE

The rupture process of the great 1989 Macquarie Ridge (M(W) = 8.1) str ike-slip faulting earthquake is examined using an empirical Green func tion deconvolution method which provides broadband source time functio ns from both body and surface waves. Recordings from a nearby, much sm aller (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 rup ture with no resolvable directivity; only minor short-period energy re lease 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 a nd no resolvable directivity from the onset to the peak of moment rele ase in the first 20 s. However, azimuthally dependent broadening of th e surface wave source functions, which extend to more than 50-s durati on, indicates a component of northeastward unilateral rupture extensio n requiring about 30-50 km asymmetry in the overall rupture, compatibl e with the northeastward asymmetry of the 1-day aftershock zone. Spect ral inversions of long-period Love and Rayleigh waves indicate a centr oid time shift of approximately 25 +/- 3 s (50 +/- 7 s duration trapez oid source) in the period range of 150-280 s, compatible with the deco nvolved surface wave source time functions. Deconvolutions using both empirical and theoretical Green functions are optimized to detect any long-period precursory radiation for periods up to about 250 s, but no convincing evidence for precursory radiation in the passband is found . The long-period surface wave phase data also do not require a precur sor.