CAN LONG-WAVELENGTH DYNAMICAL SIGNATURES BE COMPATIBLE WITH LAYERED MANTLE CONVECTION

Analyses of the long-wavelength geoid with seismic tomographic models have been providing for a long time important estimates of mantle visc osity. These estimates have nearly been derived under the assumption o f whole mantle flow. It has been commonly held that a fully impermeabl e boundary at 660 km depth is incompatible with the long-wavelength gr avity signal. On the other hand, models with whole mantle circulation, which can explain a large portion of the geoid signal, usually produc e excessive amplitudes of the dynamical topography, especially for lon g wavelengths. Using recent tomographic models together with genetic a lgorithm we have successfully demonstrated that the layered convection model can also produce a reasonable fit to the geoid, which is compar able in quality with that obtained for the whole mantle model. The lay ered model can simultaneously yield realistic amplitudes of the dynami cal topographies of the surface and the 660-km discontinuity.