Regionality of group velocities of Rayleigh waves in the Pacific and thickening of the plate

Abstract

The relationship between group velocities of Rayleigh waves and the ocean-bottom age in the Pacific is examined. The Pacific basin is divided into four regions by isochrons determined from geomagnetic lineations. A significant change in group velocities of Rayleigh waves is obtained for these four regions by the use of the least-squares method from data for 27 paths in a period range 40–90 s. The present result and other geophysical observations strongly suggest the “thickening of the oceanic plate”, and are well explained by a simple plate-thickness/age relation l(km) = 7.49 t (m.y.) 1/2 inferred from the “mantle gravity anomaly”.