SHORT-WAVELENGTH LOWER MANTLE SEISMIC VELOCITY ANOMALIES

The lower mantle seismic velocity anomalies display very smooth shapes and low amplitudes in apparent contradiction with the thermal anomalies obtained from chaotic convection models. An attempt to reconcile theoretical convection models with tomographic results is presented in this paper. Along with a coherent approach of lower mantle convection, the influences of radial and angular filtering on the shapes and on the amplitudes of anomalies have been monitored. A tremendous spreading of the radial anomalies into horizontal structures and a significant loss of amplitude of the anomalies result from this exercice. The level of the Root Mean Square of the thermal anomalies falls from several tens of degrees to values in close agreement with tomographic results. This study shows that the short‐wavelength of lower mantle velocity anomalies are dramatically hidden by the truncation level of seismic tomography. © 1990 by the Chinese Geophysical Society