The seismicity and tectonics of the Macquarie Ridge

Abstract

The Macquarie Ridge extends over 1200 km from southern New Zealand to a triple junction of the Pacific, Australian and Antarctic plates near 61 ° 30'S, 161 0 00'E. Large earthquakes occur frequently on the ridge, with an average return period of one year for an event of magnitude 6.2 or more and 10 years for one of magnitude 7.2 or more. Analysis of 16 focal mechanism solutions indicates that the direction of the principal stress is consistently horizontal, and along the northern and central ridge segments it strikes east-west. In the southern ridge segment, its azimuth is poorly defined but appears to rotate towards the northeast with increasing southerly latitude. North of 51 oS, the characteristic fault displacement is along reverse dip-slip faults, whilst south of 51 0 S, fault motion is predominantly by right-lateral strike-slip; throughout, the strike direction is parallel to the ridge axis.