Characterization of seismogenesis beneath the Tripura Fold Belt and its adjoining areas of Northeast India

Abstract

In this study, a comprehensive analysis comprising the relocation of ∼400 well-located earthquakes (M ≤ 4.9) recorded during 2013–2015 and 19-moment tensor solutions has been made. The earthquakes were recorded by 20 seismographic stations belonging to the Geological Survey of India (GSI) and National Centre for Seismology (NCS) networks. Then, the results are corroborated with the geophysical and geological investigations for the areas that need better characterization of the seismotectonics beneath the Tripura Fold Belt (TFB) and its adjoining areas in Northeast (NE) India. The sparse seismicity distribution associated with TFB shows north-south trending anticlinal ridges and synclinal valleys. These structures decrease progressively towards the south and are confined to depths between 40 and 60 km. The mixed mode of faulting at various depths indicates significant structural heterogeneity beneath TFB that dictates the earthquake strength. We conspicuously relocated earthquakes in a cluster along the Sylhet fault (SF) with a dominant northeast striking, suggesting the presence of differential structural heterogeneities with variable strengths of earthquakes located at varying depths, which in turn indicates that the seismogenesis beneath the Sylhet fault is associated with thrust mode of faulting with distinct slip component during the processes of the rupture initiation. Moment tensor solution of the area inferred two main directions: NNE –SSW and WNW – ESE, suggesting two compressive forces acting in the study area. The NNE-SSW compressional stress is dominant in this zone. This study provides deep insights into the two different structural entities, TFB and SF of NE India, that can have the potential to contribute significantly for assessing the earthquake risk potential of the region.