Locked crustal faults associated with the subducting Indian Lithosphere and its implications in seismotectonic activity in the Central Indo-Burmese Ranges, Northeast India

Northeast India is a geodynamic hotspot for tectonic activities where three different plates viz., Indian, Eurasian and Burma Plates collide and deform with respect to each other. Northeast moving Indian Plate subducting transversely beneath Burma Plate results in the formation of the Indo-Burmese Ranges (IBR). In central IBR, the north-south trending Churachandpur-Mao Fault (CMF) is situated in the east of the Mizoram-Tripura Fold belt. The northwest-southeast trending Mat River Fault or Mat Fault (MF), which is another major crustal-scale strike-slip transverse fault, upholds the movement of the CMF. In this work, seismotectonic analysis of these two active intra-plate faults which are related to the June-September 2020 earthquake series, have been discussed. It is observed from satellite imageries, earthquake data and confirmed by the field investigation that these faults are not directly involved in the generation of the earthquakes; rather epicenters are distributed in the junction between the MF and CMF. It is evident from the seismotectonic analysis that this stress is distributed through some northwest-southeast synthetic faults, located north of MF and parallel to it, close to the junction with the CMF. The focal solution of the strongest of the 2020 earthquakes, the 5.5 Mw Champhai earthquake (on 22nd June 2020 at 04:10 IST) in Mizoram shows that the principal nodal plane was aligning along MF. Therefore, it is these synthetic faults that are responsible for the earthquakes rather than the locked zone between intra-plate MF and CMF crustal faults. This juxtaposition has caused a major shift in the geodynamic regime in the central IBR. Champhai earthquake might not be the only large devastating earthquake in the region and could be followed by more major earthquakes in the future.