The objective of this review is to outline the progress made in the last four years in studies of global or large scale properties of the Earth. Work related to strictly regional structure of the crust and the uppermost mantle is described in other reports in this volume.During the previous reporting period 1971–1974 (Anderson, 1975) there was a large increase in the data base relevant to the average structure of the Earth. The number of normal modes for which eigenfrequencies have been measured increased by an order of magnitude; observations of travel times of body waves (differential travel times, in particular) were reported for several phases of key importance in constraining the core radii as well as distribution of the seismic velocities in the core and lower mantle. Quite naturally, the emphasis has been placed on construction of Earth models that would be consistent with this substantially enlarged data se
展开▼
