Structure of the upper mantle beneath the Coral and Tasman Seas, as obtained from group and phase velocities of Rayleigh waves

Abstract

Abstract Group and phase velocities for Rayleigh waves, in the period range 15–100 s, were analysed for paths crossing the Coral and Tasman Seas. We used data from 14 earthquakes recorded at the 6 World Wide Standard Stations: CTA, HNR, PMG, RIV, TAU, and WEL. By fixing the S-wave velocities at 4.65 km/s from 220 to 400 km and at 5.0 km/s for greater depths, we modelled the upper 220 km. As previous workers have found for oceanic regions, it was necessary to incorporate a significant low-velocity layer (LVL), usually centred at about 150 km, in all models. Typically the lid above the LVL has an S-wave velocity of 4.50 km/s, and the LVL a velocity of 4.25 km/s. Although the resolution of the models obtained precludes the determination of detailed Earth structure, the observations suggest that the thickness of the lid varies significantly between the “oceanic” and “plateaux” regions of Coral and Tasman Seas. It was found to be thicker beneath the Norfolk Ridge (90 km) and the Lord Howe Rise (85 km) than it ...