Author: Rafael Katzman

Publisher:

Published: 1998

Total Pages: 608

ISBN-13:

A new tomographic technique is employed to investigate the structure and dynamics of the Pacific upper mantle. We invert frequency-dependent travel times residuals of three-component turning and surface waves such as S, SS, SSS, R1 and G1 together with band-center travel times of ScS reverberations for the 2D composite structure in the plane of two Pacific corridors. The model parameters include shear-speed variations throughout the mantle, perturbations to radial shear-wave anisotropy in the uppermost mantle, and the topography of the 410 and 660 discontinuities. The image for the first corridor between Tonga and Oahu, Hawaii reveals a harmonic pattern of highs and lows having an upper-mantle thickness, a horizontal wavelength of 1500 km, and an amplitude of 3%. High shear velocities underlie each of three northwest-trending geoid swells downstream from the major hotspots of the Society, Marquesas, and Hawaiian Islands. The result along the second corridor, from Oahu and Ryukyu, also exhibits a prominent, fast region that extends beneath the entire Hawaiian swell, down to depth of 200-300 km. It is therefore implied that the topography of the swells in the central Pacific is supported by a chemical buoyancy mechanism and not by thermal buoyancy. Upper-mantle convective rolls may account for the depth extent of the fast anomalies beneath the swells.