TERRESTRIAL HEAT FLOW AND FEATURES OF THE UPPER MANTLE BENEATH THE PACIFIC AND THE SEA OF JAPAN

Abstract

The "residual gravity anomalies" in the Pacific and the surrounding marginal seas are calculated from free-air anomalies and explosion seismic results. The heat flow versus residual anomaly relation in the Pacific basin shows a clear systematic tendency which reflects the variation in thermal expansion of the upper mantle. On the other hand, the rosidual anomalies in the marginal seas, such as the Sea of Japan, are somewhat different from those in the Pacific basin. This situation implies a possibility that the upper mantle beneath the Sea of Japan is originally of high density. Its rather "soft" response to surface waves and gravity may be due to high temperature.
A contour map of the Moho depth around Japan is constructed from corrected Bouguer anomalies. The heat-flow values are used in order to remove the effect of the upper mantle heterogeneity on the observed Bouguer anomalies. The map agrees well with the explosion seismic results.