Crustal Structure of the Ninetyeast Ridge

Yu. P. Neprochnov, B. N. Grin’ko, and O. Yu. Ganzha

Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia

Received May 21, 1999

Abstract—Analysis of the data of detailed deep seismic sounding is presented. Special computer technologies
were used in order to refine the knowledge on the structure of the Ninetyeast Ridge. Generalized seismic cross
sections of the earth’s crust and the upper mantle running along the crest of the ridge and across the Mid-Indian
Basin, the ridge, and the Cocos Basin were compiled. The earth’s crust on the ridge consists of layers 1 (sedi-
ments), 2A (seismic velocity of 3.6–4.3 km/s), 2B (4.7–5.7 km/s), 3A (6.4–6.8 km/s), and 3B (7.3–7.5 km/s)
with thicknesses of 0–0.8, 0.6–1.8, 1.1–2.6, 2.1–2.7, and 2.0 km, respectively. The layers are characterized by
a vertical velocity gradient decreasing with depth from 0.5 to 0.2 s^–1. The depth of the Mohorovicic disconti-
nuity (7.9–8.0 km/s) beneath the ridge equals 12–13 km with respect to the sea level, i.e., it is the same as in
the adjacent basins. The relative elevation of the ridge over the floor of the basins and the increased crustal thick-
ness at the ridge are mostly produced by the enhanced thickness of the second layer. Variations in the seismic
velocities and thicknesses of the major crustal layers related to the block structure of the ridge are revealed.

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