Campagne Seapso 4: Etude morphostructurale de la ride de Valufa dans le bassin de Lau

The Lau Basin lies between the Lau and Tonga ridges and extends over more than 1000 km. Its width decreases from 300 km near 16 degree S to less than 100 km near 24S. It is an actively spreading oceanic back-arc basin created in the Plio-Pleistocene the Tonga Trench. The part of the Valu Fa ridge North of 22 degree S was investigated during the Seapso 4 cruise of R/V Jean Charcot in Jan 1986 and complementary data were obtained during the Papnoum transit (Apr 1987). The techniques used included multibeam bathymetry, single-channel seismic reflection, magnetic and gravity field measurements