Seismotectonic scenario of the indenting northeast corner of the Indian plate in the Tidding-Tuting Suture Zone of the Eastern Himalayan Syntaxis

Abstract

The seismicity in the north-eastern fringe of the Indian Plate in the Eastern Himalayan Syntaxis (Tidding-Tuting Suture) and adjoining areas have been studied by analyzing the earthquake data recorded by the local broadband seismograph network as well as reviewed catalog data of the International Seismological Center. The study reveals that the region is seismically active up to ~40 km depth. In contrast, the seismicity in the Indo-Burma Ranges (IBR) is observed up to a depth of ~200 km suggesting the active subduction process of the Indian plate beneath the IBR. This study suggests that the subduction process terminates north of ~270 N Latitude and the indentation process of the rigid Indian plate into south-east Asia predominantly controls the seismicity north of the IBR. The seismicity and its linkage with the existing tectonic features are critically examined in the Lohit Valley and Mishmi Hills regions. Source mechanisms of 10 earthquakes (3.5 ≤ M ≤ 4.2) are evaluated with the help of the waveform inversion technique. The results of the source mechanism study reveal that the closely spaced Mishmi, Tidding, and Lohit faults are steeply dipping thrust sheets that accommodate the large crustal shortening owing to the indentation process and clockwise rotation tectonics. The Walong fault is characterized by strike-slip motion which helps to facilitate the clock-wise rotation of crustal material around the syntaxis. Significant strain partitioning is anticipated from the variation of pressure (P) axes orientations indicating the effect of complex syntaxial tectonics.