THE GEOLOGICAL ORIGIN OF LONG-WAVELENGTH LATERAL HETEROGENEITY AT DEPTHS OF 300 - 400KM

On the basis of two three-dimensional (3-D) models of S-wave velocity, PUM0 [Hara et al., 1993] and SH425.2 [Su and Dziewonski, 1991], we sh ow that the deep roots of cratons and mid-ocean ridges provide a satis factory explanation of the pattern and amplitude of the Earth's long w avelength lateral heterogeneity in the depth range from 300 to 400 km.