Some Seismological Features of the North Macquarie Ridge

Abstract

THE recent demonstration of the existence of a ridge connexion between Macquarie Island and New Zealand, by Brodie and Dawson¹, has clarified several aspects of the regional seismology. Fig. 1 relates epicentres determined during the past 5 years by the United States Coast and Geodetic Survey in the area, to the bathymetry as presented by Brodie and Dawson. Seismicity is seen to be definitely associated with the ridge structure. There is one case (about 55° S., 163° E.) notably distant from the ridge; from consideration of P phase arrivals at Australian stations, this is believed to be a mislocated ridge shock. Thus the Campbell Plateau appears to be aseismic, at least during this period. The marked offset in the ridge at about 51° S., noted by Brodie and Dawson, could suggest a fracture zone similar to those reported along the equatorial part of the mid-Atlantic ridge by Heezen et al.². However, no epicentres have been located near this feature during the period considered.