Present-Day stress state and seismic regime in the geodynamic regions of Uzbekistan

The present-day stress state and seismic regime are comparatively analyzed for four geodynamically distinct regions of Uzbekistan and adjacent territories: the Platform region, Transition zone, Orogenic region, and Talas-Fergana region. The stress state was reconstructed from earthquake focal mechanisms using the cataclastic analysis method, considering the azimuth of maximum horizontal compression (AZgh), principal stress axes σ1 and σ3, geodynamic stress regime (IS), and Lode-Nadai coefficient (μ). Contemporary seismicity was characterized by normalized seismic activity log10 A(M=3.3), Gutenberg-Richter b-value, and thickness of the seismically active layer H. The regions show pronounced differences in stress orientation, directional consistency, stress regime, and seismicity. Talas-Fergana has the highest directional stability, whereas the Transition zone has the greatest orientational and depth-dependent heterogeneity. The Orogenic region has the highest seismic activity, while the Platform region has the lowest activity and highest b-value. Talas-Fergana combines the lowest b-value (0.69) with one of the largest seismically active-layer thicknesses (20.2 km). No one-to-one relationship exists between individual stress and seismicity parameters; regional geodynamic differentiation is expressed most clearly by characteristic combinations of independent parameters.

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