1980 - National Institute of Oceanography

Seismic profile (4.5 kjl sparker) on the continental slope off Cochin.
(c) Off Bombay: In this region the clay is about 15 m thick near the shore
and at about 20 m depth. It thins out to less than one metre at about 70 m depth
at a distance of about 140 km from the coast. The transparent layer in this region
reaches a maximum thickness of 50 to 60 m. Based on seismic records, four strata of
different ages are recognisable. A depression is seen at about 90 m depth and a series
of faults are also noticed on the edge of the continental shelf.
3. Acoustic masking due to gases
The shallow seismic and echosounding records of the clays on the inner and
middle shelf off Bombay, Konkan, Karnataka and Kerala are marked by turbidity.
In some cases, the turbidity which is due to acoustic masking by gases extends over
50 to 60 km and covers more than 2500 km 2 . The cores collected in the area show
bubbles and fissures in the turbid zone. The gas from these bubbles and fissures
was predominantly methane with traces of higher hydrocarbons. The gases were formed
by the degradation of large quantities of organic matter produced by increased
productivity or because of a greater influx of organic matter on the recent past.
4. Magnetics
(a) Off Cochin: The nearshore area between Cochin and Quilon is marked
by a few high amplitude anomalies (about 200-300 gammas). Besides these anomalies,
the rest of the shelf and slope appears to be magnetically smooth. Over the
39