Rupture process of the MacQuarie Ridge Earthquake of May 23, 1989

Abstract

Broadband body waves recorded at 15 digital seismic stations worldwide are used to study the rupture process of the May 23, 1989 Macquarie Ridge earthquake. The centroidal solution (strike 211°, dip 86°, rake 180°, and depth of 10 km below the seafloor) indicates shallow rupture with pure right‐lateral strike‐slip motion along the Pacific‐Australia plate boundary, in agreement with motion predicted by plate tectonic models. The total seismic moment is 13.4×1020 Nm, 80% of which was released in the first 24 s of the rupture process. Modeling favors a bilaterally propagating rupture with slightly different dip and rake for the northward and southward fault segments and similar moment release along both directions. The estimated fault length is quite short, about 90 km, and the derived stress drop of 180 bar and average displacement of 17 m are unusually high. The bathymetry in the epicentral region shows topographic segmentation of the ridge, possibly indicating fault segmentation which confines ruptures to short segments.