Southern limits of major earthquake ruptures along the Himalaya between longitudes 75° and 90°E

Abstract

The ruptures responsible for major earthquakes along the Himalayan Convergent Plate Margin (HCPM) occur in a strikewise oriented zone of frictional failure and relative slip in a buried detachment along the upper surface of the Indian Shield rocks subducting under the Himalaya. The southern limit of the rupture zone is a geotectonic lineament whose geographic location is important in assessing risk due to earthquakes. A major part of this article is taken up in arguing that the available macroseismic and instrumental evidence for the 1934 Bihar-Nepal earthquake is consistent with the view that the rupture which caused it occurred in the detachment mostly under the Lesser Himalaya northward from the vicinity of the surface trace of the Main Boundary Thrust (MBT). Since a similar location has been inferred by others for the 1905 Kangra earthquake rupture, a basis arises for postulating that, over more than half of the length of the HCPM between 75% and 90° E longitudes, the ruptures responsible for major earthquakes lie in the detachment with their southern limits geographically similarly close to the surface trace of the MBT. This includes the nearly 700 km long seismic gap between the 1905 and 1934 ruptures.