SECT. 1] 



GRAVITY AT SEA 



171 



from 800 km to 900 km east of Suva, Fiji. Thus there seems to be a conflict 

 between the seismic and the gravity data. In Fig. 31 the boundaries in the 

 regions where no seismic data exist have been adjusted and an almost masked 

 (seismically) interface is assumed in the trench region in order to compute a 

 gravity curve which fits the observed data. In this way the conflict between 

 the seismic and gravity data can be resolved. 



RIDGE 



GRENADA BASIN 



LESSER 

 ANTILLES 



BARBADOS 

 RIDGE 



KILOMETERS EAST OF LONGITUDE 60° W 

 -300 -200 -100 O 



Fig. 29. Structure section across the gravity-anomaly belt of the Lesser Antilles near 

 Barbados computed to fit the seismic and gravity data. (After Sutton, Talwani and 

 Worzel, 1960.) 



The reader is again referred to Fig. 17 for a view of the structure of a trench 

 complicated by a continental margin and an adjacent mountain range. 



F. Summary 



The advent of gravity meters capable of making gravity measurements on 

 surface ships, even though at present they require moderate seas in which to 

 operate, ushers in a new era in the measurement of gravity at sea. We can ex- 

 pect a vast increase in the data of gravity at sea and a great deal better insight 

 into the most "normal" part of our globe. 



Most authors have computed a mass distribution to account for the observed 

 gravity anomalies on the assumption that fluctuations of the M-discontinuity 

 can account for the anomalies, at least after one has accounted for the sedi- 



