ABSTRACT
An accurate account of riverscape changes can be prepared only by using the oldest topographic maps available, which are not older than a few hundred years in general. For the Brahmaputra River in Assam, the oldest accurate status is that of the year 1915. However, due to the high-density geophysical data archive available with oil industries, it is possible to extend the historical reach. Uphole and refraction-based seismic data give lateral thickness variation of the weathered zone and seismic wave velocities through the layers at shallow depths. Using velocity as a discriminator, it is possible to identify the channel paths of the Quaternary period. This can help identify the direction of migration of the channels, which, in turn, can be interpreted in terms of slope variation of the valley floor. The tilt of the valley floor can be correlated with active tectonic elements. This kind of inferential reasoning was used for selective oil windows having geological complexities to study the impact of neotectonics on river dynamics. Moreover, a new tectono-morphogenic micro-zonation scheme was evolved.
