Occurrences of damaging earthquakes between the Himachal and Darjeeling Himalayas: Tectonic implications

Detailed analysis of intensity for ten damaging historical earthquakes in the central arcuate belt between the Himachal and Darjeeling Himalayas was carried out in the backdrop of isoseismal eccentricity, source depth and Indian plate obliquity. Results indicate that the elongated axes of the isoseismals and strike of ruptures for shallow earthquakes are almost parallel with strike of the Himalayan arc, and clearly conformable with the obliquity. An empirical power law relationship between eccentricity and focal depth established under the present study illustrates that the deeper events are more influenced by the bending of the penetrating Indian lithosphere, whereas the shallower events are principally controlled by the obliquity. A positive correlation between eccentricities and obliquity obviously supports this inference. The present study further reveals that the constant decrease in Indian plate obliquity from Himachal to Nepal-Bihar Himalaya is well compatible with the graben structures and horizontal shearing along this arcuate segment.