THE NATURE OF THE MOHOROVICIC DISCONTINUITY (Mo-ho chieh-mien ti hsing-chih),

The paper discusses the various theories on the nature of the Mohorovicic discontinuity and the difficulties encountered by the phase-change hypothesis. By examining the velocity distribution data recently obtained by use of seismic body and surface waves, the following conclusions can be made 1 The Mohorovicic discontinuity, either under the continents of the oceans, cannot be interpreted as a surface of phase transition. 2 The chemical composition of the upper mantle is not homogeneous in the vertical direction. The low-velocity layer in the upper mantle is probably caused by a change in composition rather than by the temperature effects. 3 The top surface of the asthenospheric low-velocity layer is deeper under the oceans than under the continents. 4 The chemical composition of the upper mantle, according to the data of radioactive measurements, may be some mixtures of eclogites or other ultra-basic rocks, their change of velocity due to temperature effects being very small. Author