| Abstract Submission No. | ABS-3.1-0157 |
| Title of Abstract | Seismotectonics of the Kopili Fault Zone, Northeast India: Insights from a 3D Seismic Body-Wave Velocity Model and Stress Field Analysis |
| Authors | Rabin Das* |
| Organisation | North-East Geophysical Research Laboratory, IIG, Shillong- 793005 |
| Address | NEGRL, IIG, Shillong Shillong, Meghalaya, India Pincode: 793005 E-mail: rabingeophy@gmail.com |
| Country | India |
| Presentation | Poster |
| Abstract | The Kopili Fault Zone (KFZ) is a seismically active intra-continental fault system located at the juncture of the Himalayan Arc and Indo-Burman Ranges, playing a crucial role in regional tectonics and seismic hazard. Despite several documented moderate to large earthquakes, understanding of the fault's subsurface structure and stress regime remains limited due to crustal heterogeneities. This study integrates local earthquake tomography and focal mechanism-based stress field analysis to elucidate the 3D seismotectonic framework of the KFZ. Using seismic data from the Indian Institute of Geomagnetism (IIG) and the National Centre for Seismology (NCS), we jointly inverted P- and S-wave arrival times to generate crustal velocity models (Vp and Vs), revealing significant lateral and vertical variations. A prominent near-vertical, NW-SE trending low-velocity anomaly extends to 30 km depth and is interpreted as a damaged fault core. Earthquake hypocenters cluster along its margins, suggesting strain localization at the interface between this weak fault core and the surrounding rigid crustal blocks, highlighting fault zone heterogeneity as a key control on seismicity. Additionally, stress-field analysis derived from focal mechanisms indicates a predominantly compressional regime with the maximum horizontal stress (SHmax) oriented NNE-SSW, consistent with Indian plate convergence. Faulting is mainly strike-slip with a significant thrust component, aligned with observed moment tensors. Localized rotations of principal stress axes near the fault imply complex stress partitioning influenced by crustal anisotropies and fluid presence. These results support a unified seismotectonic model wherein KFZ seismicity is driven by interactions between a fluid-modified weak fault core and regional compressive stresses, advancing understanding of fault mechanics and seismic hazard in this densely populated, tectonically complex region of Northeast India. |
| Keywords | Kopili Fault Zone, North-East India; Seismotectonics, Velocity Tomography, Focal Mechanism Solutions, Seismic Hazard |