Island Arc System in Andaman Sea

A sub-bottom profiler survey of the Andaman Sea was conducted as part of the marine geophysical program of the U. S. Coast and Geodetic Survey during the International Indian Ocean Expedition. The survey lines were run at right angles to the predominantly north-south tectonic lineations of the island arc system. A 20,000-joule sparker, energized every 4 sec, was used as a sound source and was towed about 100 m behind the ship. A 20-hydrophone array received the reflected signals, which were recorded both on a paper strip chart and magnetic tape. The sub-bottom profiler sections and the marine gravity and magnetic measurements augmented knowledge of the geology of the island arc system; the linear structural belts on land were traced through the Andaman Sea by geophysical methods. The structural development of the island arc system from east to west can be traced, based on available continental and marine data. It was possible to delineate the major segments of the island arc system through a distance of 600 nautical mi (1,110 km) in the Andaman Sea, specifically, the foredeep, outer sedimentary island arc, interdeep, inner volcanic arc (and rift valley), and backdeep.