Active tectonics in the Assam seismic gap between the meizoseismal zone of AD 1934 and 1950 earthquakes along eastern Himalayan front, India

Abstract

The Assam Seismic Gap has witnessed a long seismic quiescence since the Mw ∼8.4 great Assam earthquake of AD 1950. Owing to its improper connectivity over the last decades, this segment of the Himalaya has long remained inadequately explored by geoscientists. Recent geodetic measurements in the eastern Himalaya using GPS document a discrepancy between the geologic and geodetic convergence rates. West to east increase in convergence rate added with shorter time span earthquakes like the 1697 Sadiya, 1714 (Mw ∼8) Bhutan and 1950 (Mw ∼8.4) Tibet-Assam, makes this discrepancy more composite and crucial in terms of seismic hazard assessment. To understand the scenario of palaeoearthquake surface rupturing and deformation of youngest landforms between the meizoseismal areas of Mw ∼8.1 1934 and 1950 earthquakes, the area between the Manas and Dhanshiri Rivers along the Himalayan Frontal Thrust (HFT) was traversed. The general deformation pattern reflects north-dipping thrust faults. However, back facing scarps were also observed in conjugation to the discontinuous scarps along the frontal thrust. Preliminary mapping along with the published literature suggests that, in the eastern Himalayan front the deformation is taking place largely by the thrust sheet translation without producing a prominent fault-related folds, unlike that of the central and western Himalayas.

Paleoseismological Studies in India (2016-2020): Status and Prospects

“…The investigations made by Pandey et al (2018a) between the Manas and Dhanshiri Rivers along the HFT in the NE Himalaya ( Fig. 5B) suggest that the general deformation pattern reflects north-dipping thrust faults.…”

Active tectonics of Himalaya, rift basins in Central India and those related to crustal deformation at different time scales

“…Towns of Assam like Tezpur, Masamari, Tumuki, Dhekiajuli, Nagaon, Bomdila, Udalguri, Seppa, Hajoi, Behali, Guwahati, and Itanagar that are located ~60-130 km from the source zone have been said to experience very strong to moderate ground shaking, while towns like Jorhat, Ziro, Mokokchung, Dhubri, and Kokrajhar that are located at a distance of 130-300 km from the source will experience low ground shaking. Pandey et al (2018) investigated the active tectonics in the area lying between the Manas and Dhanshiri Rivers in upper Assam, seismically located within the meizoseismal zones of 1934 and 1950 earthquakes along the eastern Himalayan front, India, previously designated as the 'Assam Seismic Gap'. In order to understand the scenario of paleoearthquake surface rupturing and landform evolution along the Himalayan Frontal Thrust, with a relation to the deformation of these landforms by previous earthquakes, they studied active tectonics of the region using photogrammetric techniques and high resolution satellite imageries together with field survey using RTK-GPS (Real Time Kinematics-Global Positioning System).…”