Integrated stress and strain characterisation of the Himalayan-Tibetan collision zone using earthquake and geodetic data

The Himalayan-Tibetan Collision Zone (HTCZ) is one of the most geodynamically active regions on Earth, shaped by the continuous collision between the Indian and Eurasian plates. This study analyzes the prevailing crustal stress and deformation patterns across the HTCZ by integrating earthquake focal mechanism solutions (FMS) with velocity data from the geodetic Global Navigation Satellite System (GNSS). Inversion of FMS data, using iterative and damped methods, reveals a dominant N-S oriented compressional stress with low-angle plunges along the Himalayan Arc. In contrast, the Tibetan Plateau exhibits a combination of strike-slip and normal faulting with WNW-ESE stress orientations. To better understand deformation pattern, GNSS-derived velocity data were inverted using a modified weighted least-squares approach to estimate regional strain rates. The resulting dilatation strain rate map too highlights the significant crustal shortening along the Himalayan Arc, while the Tibetan Plateau displays extension. However, the maximum shear strain rates are primarily attributable to strike-slip faulting in Tibetan region. Additionally, the second invariant strain rate map indicates the highest deformation concentrations in the central Himalaya and the eastern Himalayan syntaxis. The maximum horizontal compressive stress orientations (SHmax) derived from FMS closely align with the maximum horizontal shortening strain-rate orientations (epsilon Hmax) inferred from GNSS velocities. The strong correlation between SHmax and epsilon Hmax within the 75 degrees E to 95 degrees E longitude suggests the high elasticity of the central segment of HTCZ. However, the noticeable clockwise rotation of SHmax and epsilon Hmax over the eastern segment underscores the presence of a viscous lithosphere beneath the Tibetan Plateau. These findings provide valuable insights into the Himalayan stress-strain regime and enhance our understanding of crustal deformation processes in this highly dynamic tectonic zone.