Seismogenesis of earthquakes in the Dhubri-Chungthang fault zone, India

For eastern Himalayan segments the Shillong block is distinguished by clustered seismicity along the Kopili Fault Zone (KFZ) and the Dhubri-Chungthang Fault Zone (DCFZ). The foreland seismicity patterns of the KFZ and DCFZ seem to penetrate the higher Himalayan mountain belts. To understand the ability of the DCFZ in generating future great earthquakes and its role in segmentation of Himalaya which affects regional seismicity pattern, a network of 54 broadband seismic stations was installed in two phases (2018-2023, 2023-continuing) covering Sikkim and Foreland Basin along the DCFZ. Preliminary results suggest concentrated seismicity along the DCFZ. Earthquakes are of mid-crustal origin, akin to results from earlier experiments. Focal mechanisms are showing dominantly strike-slip nature of the fault zone. Crustal structure obtained using receiver functions have shown a very complex crust with prominent offsets and overlaps. The thick sedimentation in foredeep is revealed with large amplitude arrivals close to 1 s. Moho arrivals show a thick crust beneath Himalaya and its foredeep. Highly deformed middle crust show presence of dipping and anisotropic layers, evident in the backazimuthal stacks of receiver functions. The seismicity and crustal deformation with presence of dipping and anisotropic structures suggest presence of a sheared fault zone, though extent of this zone remains unclear in the preliminary results. Ongoing experiment with continuous monitoring of seismicity of DCFZ, will help to resolve critical issues, like depth extent, dominant fault mechanisms and penetration of the DCFZ within the Himalaya, its role in segmentation of the Himalayan arc and defining seismogenic boundaries and rupture zones of possible major earthquakes.