Regional and azimuthal dependence of phase velocities of mantle Rayleigh waves in the Pacific Ocean

Abstract

The lateral heterogeneity and azimuthal anisotropy of the upper mantle in the Pacific Ocean are investigated by analysing Rayleigh wave phase velocities in the period range 60–200 s. Rayleigh waves at periods below 150 s travel fast in the direction parallel to the present-day plate motion. Rayleigh wave velocities at longer periods show a similar azimuthal dependence in most parts of the Pacific. The average magnitude of the velocity-anisotropy in the Pacific Ocean changes from 1% at 60 s to 0.4% at 200 s. The azimuth-independent phase velocities increase with the increase in age of the sea floor in the period range 60–120 s, but the correlation is weak at longer periods. The trade-off between the lateral variation and the azimuthal variation is weak except for marginal places of the studied area.