Gravity survey was carried out to clarify the basement topography of the Kathmandu Valley which is filled with the Quaternary lacustrine sediments. A gravity anomaly map is produced from 112 gravity measurements within a major part of the Kathmandu Valley and a basement contour map is presented based on depth calculations along two sections.
The maximum depth of the basement is estimated to be a little more than 650m from the present surface. Two distinct troughs of basement are detected in the central part of the Valley. The troughs may be a part of fossil valleys of what Hagen (1968) proposed as the Proto-Bagmati River which supposedly had drained south-south-westerly across the Kathmandu Valley during the Plio-Pleistocene time.