The Great MacQuarie Ridge Earthquake of 1989 Introduction

On May 23, 1989, a great earthquake struck a remote region of the South Pacific Ocean between New Zealand and Antarctica. The nearby islands are Macquarie Island, about 300 km south of the epicenter, and Campbell Island, almost 600 km east of the epicenter; the latter experienced shaking with intensity V. Fortunately, both islands are sparsely inhabited and litfie damage or injuries were reported. In addition, only relatively small tsunamis were recorded on tide records in Australia. We can all take comfort from the fact that tiffs great earthquake had litde impact upon the acfivi6es of the nearby communities, yet it has had substantial impact within the global seismological and tectonic commanit/es. With respect to seismology, the 1989 Macquarie Ridge event is the largest earthquake of the decade. Moreover, this earthquake provided a "test" for the rapid exchange of digital seismograms from the new-generation global seismographic stations. With respect to tectonics, this earthquake occurred in a somewhat unusual tectonic set•g where a new subduction zone may be starting. A special session on the great 1989 Macquarie Ridge earthquake was held at the 1989 Fall meeting of the American Geophysical Union. This special section is based largely on papers presented at the AGU meeting, in particular the papers by: Ekstrom & Romanowicz, Satake & Kanamori, Tichelaar & Ruff, Anderson, Park, and Gross & Chao. In addition, this special issue contains contributions from Braunmiller & Nabelek, and Houston. These eight papers cover many different aspects of the great Macquarie Ridge earthquake, i.e., moment tensor, focal mechanism, source time function, rupture process, stress-drop, ultra-long period characteristics, and seismotectonics. Rather than preview the research contributions in the following papers, I turn my focus to the seismological envkonment and tectonic context in which this great earthquake occurred.