ANALYSIS OF MULTICHANNEL SEISMIC-REFLECTION AND MAGNETIC DATA ALONG 13-DEGREES-N LATITUDE ACROSS THE BAY OF BENGAL

Analysis of the multi-channel seismic reflection, magnetic and bathyme tric data collected along a transect, 1110 km long parallel to 13-degr ees-N latitude across the Bay of Bengal was made. The transect is from the continental shelf off Madras to the continental slope off Andaman Island in water depths of 525 m to 3350 m and across the Western Basi n (bounded by foot of the continental slope of Madras and 85-degrees E Ridge), the 85-degrees E Ridge, the Central Basin (between the 85-deg rees E Ridge and the Ninetyeast Ridge), the Ninetyeast Ridge and the S unda Arc. The study revealed eight seismic sequences, H1 to H8 of para llel continuous to discontinuous reflectors. Considering especially de pth to the horizons, nature of reflection and on comparison with the p ublished seismic reflection results of Curray et al. (1982), the early Eocene (P) and Miocene (M) unconformities and the base of the Quatern ary sediments (Q) are identified on the seismic section. Marked change s in velocities also occur at their boundaries. In the Western Basin t he acoustic basement deepening landward is inferred as a crystalline b asement overlain by about 6.7 km of sediment. In the Central Basin pos sibly thicker sediments than in the Western Basin are estimated. The s ediments in the Sunda Arc area are relatively thick and appears to hav e no distinct horizons. But the entire sedimentary section appears to be consisting of folded and possibly faulted layers. The comparatively broader wavelength magnetic anomalies of the Central Basin also indic ate deeper depth of their origin. Very prominent double humped feature of the 85-degrees E Ridge and broad basement swell of the Ninetyeast Ridge are buried under about 2.8 km thick sediments except over the pr ominent basement high near 92-degrees E longitude. The positive struct ural relief of the buried 85-degrees E Ridge in the area is reflected in magnetic signature of about 450 nT amplitude. Flexural bulge of the 85-degrees E Ridge and subsidence of the Ninetyeast Ridge about 24 cm my-1 rate since early Eocene period have been inferred from the seism ic sequence analysis.