| Abstract Submission No. | ABS-3.1-0191 |
| Title of Abstract | Spatial Clustering and Stress Inversion of Focal Mechanisms of Central Himalayan Seismicity (1980-2025): Evidence for Partitioned Deformation and NW-SE Compression |
| Authors | Udaya Bahadur Thapa Kshetri*, Ram Krishna Tiwari, Eak Raj Poudel, Rudra Prasad Poudel, Harihar Paudyal |
| Organisation | Central Department of Physics, Tribhuvan University, Kathmandu |
| Address | Navaratna Tole, Shanti Marga Bharatpur,Chitwan, Bagamati Province, Country: Nepal, India Pincode: 44200 E-mail: udaya.kshetri@bimc.tu.edu.np |
| Country | India |
| Presentation | Poster |
| Abstract | The ongoing continental collision between India and Eurasia renders the Nepal Himalaya one of the most seismically active regions on Earth. However, the spatial partitioning of deformation and the state of stress within this complex orogen remain incompletely resolved. This study employs an integrated machine learning and mechanical analysis workflow to delineate seismogenic zones and quantify their stress regimes using the Global Centroid Moment Tensor (GCMT) catalog. From 131 events (Mw≥4.0) between 1980-2025, we first classified earthquakes into thrust (n=38), normal (n=40), strike-slip (n=22), and oblique (n=31) types. K-means clustering analysis revealed 10 spatially distinct seismogenic clusters. Formal stress inversion was performed on each cluster to determine the principal stress orientations and the stress ratio (R). Our results reveal a dominant NW-SE compressive stress field (σ₁ azimuth: 299-316°) driving thrust and strike-slip faulting in the orogen, challenging the simplistic view of pure N-S compression. Normal faulting clusters in Tibet confirm E-W extension but show complex, variable extension directions (σ₃ azimuth: 92-255°). Strike-slip faulting exhibits a uniform NW-SE compression. Oblique faulting clusters represent a critical transition zone between these regimes. The stress inversion misfits were low (11-30°), confirming robust solutions. This analysis provides a quantitatively refined, mechanics-based model of Himalayan tectonics, revealing a highly partitioned and complex deformation field that must be incorporated into future seismic hazard assessments. |
| Keywords | Nepal Himalaya, Seismotectonics, GCMT Catalog, K-means Clustering, Stress Inversion, Himalayan-Tibetan Orogeny |