Abstract
A study of aerial photographs taken before and immediately after the Great Assam Earthquake of 15th August 1950 revealed that the event had caused extensive landsliding in the northeastern India, including parts of catchments of Dihang and Subansiri rivers. Examination of the photographs of the same areas taken during 1959-60 and 1976-77 showed, that majority of the slopes that failed as a result of the earthquake, got stabilised to a large extent and some fresh landslides occurred during the period in a few areas.
Air-photo study shows that (i) the highly jointed nature of the Miri Quartzite has contributed to the maximum incidence of landslides in any particular lithological unit. (ii) The Main Boundary Fault and the system of faults parallel to it, in the Subansiri catchment have been reactivated during the Assam earthquake. (iii) In Dihang catchment, the MBF, and the Siang fracture have been reactivated.
In view of the possibility of fluid pressure exerted by impounding large quantities of water triggering off a major earthquake, it is suggested that construction of very large dams be avoided, even though the region has a very high hydel power potential.
